Keep in mind that this is all my opinion. Some things on this list you might not think of as an issue, but I myself take issue in.
Personally, +2 is trash. It's nothing more than trying to "encourage" people to grind to higher tiers.
- People start the game. They see tanks two tiers higher and cannot effectively combat them.
- They think "When I'm in that tank, I'll seal club in that tank!"
- When they get that tank, they get seal clubbed by tanks two tiers higher.
- So they try to get to that tank, until tier 10 when they finally get to seal club useless tier 8s.
It is endlessly frustrating to have to play differently simply because some algorithm decided you'd be significantly worse than the opponent. I can accept being outplayed, but I cannot accept being significantly worse than my opponent simply because they got lucky enough to be top tier.
I believe that single tier matches are the most fun, simply because no one has a significant advantage for no explicable reason aside from getting lucky.
The fact that a lot of the recent premium tanks(Centurion 5/1, Progetto 46, T26E5, Firefly VC, King Tiger) are better than their tech tree counterparts is not very convincing in terms of this game lacking P2W mechanics. A T26E5 will almost always win against a T32, and a Centurion 5/1 is a strictly better Centurion I. In my opinion, a premium vehicle shouldn't be better or worse than a tech tree vehicle. Rather, it should be as good or have a gimmick that differentiates the vehicles.
While you cannot directly buy 'premium' ammunition, you can however buy a premium account, which allows you to buy more premium ammunition. In effect, only those who can buy premium account are able to consistently use premium ammunition.
HE-focused guns Type 5, KV-2, FV4005 for example.
Now, this is a rather difficult thing to balance. On the one hand, a Kranvagn in a perfect hull down position is insanely difficult to eliminate without HE splash damage. On the other, the Kranvagn is liable to get frustrated as well, due to being unable to combat the HE splash effectively.
It is insanely frustrating to have a Type 5 Heavy or FV4005 do 500 damage to you by simply pointing and clicking. However, it would also be frustrating to have a big fucking gun and do very little damage. Honestly, I think a flat-out removal of HE-focused guns would be better, as it's difficult to impossible to balance this kind of gun.
Now, this is a hot topic for sure, and has been covered extensively. In my opinion, the implementation of the artillery class was a mistake from the get-go.
The fact that a class can hit you from pretty much anywhere on the map with zero counterplay, aside from simply hiding and not getting spotted, is insanely agitating. I've lately come to the conclusion that WG simply loves zero counterplay mechanics, as they have implemented a CV rework in World of Warships that basically makes the CVs a class that can spot on its' own and do damage at the same time, with no counterplay whatsoever aside from simply not playing the game.
Now, this is the most complicated issue on this list. On the one hand, if you couldn't stealth fire, certain vehicles would be made incredibly difficult, if not impossible, to play. Vehicles like the M56 Scorpion would not be playable whatsoever if they were spotted when they fired regardless of what concealment they had. On the other hand, being shot at by a tank you cannot see is insanely frustrating.
I believe that a 'fire and manoeuvre' mechanic could work rather well, where you get spotted if you fire out of the same bush twice would work rather well.
New Player Experience
Now this is the most objectively worse issue on this list thingy. A new player has almost no information to go on aside from a rather lack-lustre tutorial, and is subject to some of the most sealclubby vehicles known to man. From the FCM PaK 400 Meter View Range to the Pz. B2, the new player has very little chance against some of the seasoned players in their low tier premiums, chock full of premium ammunition, premium consumables, 7-skill crews, and equipment. I honestly don't think I need to explain more, as even the briefest glance at the low tiers in World of Tanks is enough to convince most people to quit the game entirely.
I personally want the game to do well, and it saddens me that so many issues remain unfixed or are not seen as issues by the developers.