I know this thread is going to get bombarded by videos of necros crushing newbies and there are some good necros out there but comparatively, they suck in pvp.
Even the best necro's would struggle against the top tier players of other classes. Even if I see some super-elite necro in BG's I'm hardly worried but if I see a general+ of DK/Temp/warden then I've got to be on top of my game or my team will get crushed.

Necro's have almost no good crowd controls or buffs

Necro is almost entirely a tanky class when we didn't need any more tanks. you could build for damage but you have no good burst heals or evasive skill like ball of light or cloak. the class has no good cc, the totem is super avoidable (hell sometimes i purposely get feared by it so i can have a break free on my terms vereses having to break free while taking burst damage).

the blast bones is cool but its timing is completely a variable, unlike the other burst skills the other classes have that are exact timing.

one caveat is that necros do seem to do alright in IC where corpses are easy to make.

Necro's have two skills that function identically by tethering corpses which is just lazy. it should just be one skill with a morph that heals and one that damages, the stam and mag regen accordingly. then give necro a decent single target cc.

the colossus is probably the best skill it has for pvp if your team works together. Maybe that's why this class has terrible crowd control options because you kind of need your teammates to supply the cc and roots to maximize this ults damage. there are a couple cc options outside the class but not many. vamp drain probably being the best. but you gimp yourself to have vamp.

Necro did have that narly bashing collosus build but now that morph hasn't been seen in pvp since the nerf.

The colossus is interesting but it synergizes poorly with a key bone tyrant skill, bitter harvest, and especially necrotic potency Morphy. you cant gen ult during colossus so the ult gen part of the skill becomes worthless. no other skill gets worse when used with its skill line ultimate. This skill should increase the bone colossus time when used while bone colossus is active to make up for it losing half its effect (i don't care if it's even 1 sec per corpse). I know the heal is health-based and gets stronger but honestly, it's still hardly worth it. better to wait until the transformation ends then use it again for a big ult gain, until then it's just taking space up on your bar.

A skill that does synergies well with the colossus ult is the scythe but its practically worthless until you transform (besides solo PVE but we're talking pvp here). unlike other class melee skills that heal this skill pulls from two different stat pools, stam/Wcrit/Wdmg and health. other class melee heal based on damage so you can further poor your stats into damage while getting a survivability bonus. this skill is a *** hybrid of brawler and sunshield but worse than both. Honestly, it would be nice if it had some jabs elements to it where it does bonus damge to a single enemy. maybe like a guaranteed crit on one enemy or maybe have the skill do bonus crit damage to synergize with death knell and actually reap some enemies with your scythe. also, tanks usually have low crit chance so this skill would benefit both tanky bulds or damage builds in different ways that don't necessarily stack with itself. To clarify you can for crits and have your scythe crit enemies hard but the heal is poor, or you can build tanky (like you can now) and the heal is great but you wouldn't crit often.

Reanimate... *sigh* an ultimate that is actually worse than a passive (in my opinion). Templars with full alliance war support passives can bring back a player pretty damn quick with full health, this ult costs 300 and brings your allies back with half health to get ganked again. maybe in group fights in cyrodil this shines but that's it. Zos, recently you changed all the resurrection skills to be health % based instead stating that they overperformed in rare instances and were pointless in most others, that statement fits this ult perfectly. Reanimation is a staple of the necro class but it could be way more universally beneficial. Here are some ideas off the top of my head:
-reduce the cost to 100 and reduce the resurrections to one, so you can use it more often if you need to resurrect 3 players at the same time chances are your so screwed that bring back three players with half health is just feeding the enemy AP.
-allow the necro to use the skill in death to resurrect itself. if mannimarco can resurrect himself, why can't we. it would cost ult all the same.
-resurrect players with full hp
-resurrect players with a shield
-place an HoT on living players in area so it at least has a use outside of resurrecting
-give it a slotting bonus, like 8% magika so that magcros can at least get the same bonus from the necromancer set as sorcs,nb's, and wardens. it's silly that the class of the same name gets the lowest bonus.
-a slotting bonus that grants mitigation to help you out when your enemy figures out that your healing and decides to focus you.

expunge- looks goon on paper but is awful in practice. wardens have a purge every 5 seconds for free plus an awesome buff PLUSS recourses. yet this kill costs life to just purge twice and about nothing else. with the warden's betty netch reasoning this skill should be free and heal you for a small amount instead. I've never seen two skills that are so insanely far apart on the spectrum of usefulness, it blows my f*cking mind. 2k health isn't much for the tank necro but if you're getting dotted up as anything but a tank you're pretty much killing yourself now instead of a slow death, especially with the nerf to dots, it's hardly worth it. maybe expunge can give a buff (necros have almost none) like minor berserk, which is rare among other classes. or make base expunge cleanse all negative effects since that's really all it does and it costs health.

the skeletal pets are pretty useless too, they give your enemy a bit of targeting trouble but good opponents will tab target you anyway. They cost so much to do so little. also, the archer pet looks stupid when it runs right next to your enemy and lobs arrows in a tiny arc.

Avid boneyard- this skill I have seen cause players grief but mostly just newer players. with the jewelry enchant that boosts synergy effects, this can be a deadly combo but the are some downsides, it's obvious. this skill usually gets me once but only once, when I see the aoe drop again a roll away before the synergy goes off. I do see necro nb combos where the nb is invis next to the enemy and macros the synergy the second the necro drops the boneyard but if that is really such a problem then the NB temp combo is way way worse. sometimes all my death recap says is gravity crush for 30K and nothing else, that's because the macro spamming nb already activated the gravity crush before the skill itself could do any damage.

My final point is, could giving this class an escape ability be so bad? let nontank necros shine in PVP. I've had some thoughts on this. what I thought would be cool is a skill that would make the next hit "instantly" kill you but instead of actually being dead you could spirit walk a short distance before resurrecting at the same level of stats you had when you "died". you can't do anything else while spirit walking and maybe give your enemy a visual cue like a wisp. maybe also give a magika cost debuff like a ball of light. another idea is to have your character tunnel underground taking damage from only ground placed aoe's before popping out. Another idea I had is making the colossus transformation charge while you sprint knocking enemies back and making you immune to snares and roots so damage based necro has a great escape option but not one they can use frequently. of course, this type of skill would need to be balanced to be on par with other evasive skills but in my opinion, there are so few evasive skills that would be nice to have one more to shake up combat. right now you can pretty much treat a necro as any other tanky build, they're gonna hold block when they feel the heat and alternate damage and heals when necessary. so boring, at least a dk may do something screwy like petrify or leap and wardens got shalk and an almost eternal blizzard.

So, in conclusion, I know the necro has been overperforming in PVE but in pvp it is pretty much a dud. I'm not suggesting it should be better than other classes but nontank necros should be a threat in pvp outside of ball zerg bots which any class could do well if not better. obviously, if necros got every buff I suggested they would be wicked op but they definitely need some love in the pvp department. Also, a lot of my suggestions are to buff skills that are really bad and unused in late-game pvp. I don't think this would make necros overpowered as much as give them more options. Also because necros are so strong in pve situations the buffs they get shouldn't affect pve conent greatly, like adding an evasive skill or an extra cc.

Yet again, Necro needs PVP love because no one fears the reaper.