[Erendil]

Here's my top 5:

1. If I could only choose one I'd say BFR's. Even though they're not the monstrosities that they were when first introduced, the damage was done long before they were nerfed to their present state, and they still have a few characteristics that make them really hard to balance, quirky, nonsensical, and incredibly annoying. Rechargeable shields, being a flying tank, vulnerability to infantry, the camera shake effect on nearby units, faster shield charge when sitting still, ability to run underwater, etc. Their addition fundamentally changed the way ground battles were fought for the worse, and PS never really recovered from the damage they did.
2. SOE's horrendous development, support, and anti-hacking efforts since.... oh, 2006.
3. 3rd Person view for infantry. Camp camp wallhumpwallhumpplasmaplasmaplasmaboomerboomer. blah blah blah...
4. Air Cav. With Air Cav you can either annihilate (Reaver) or bypass (Mossie) just about everything between you and your objective. They're way too versatile, and made a lot of other playstyles/tactics obsolete.
5. BR40. Actually, anything above BR23. 23 is borderline.

Here's a bunch more in no particular order. None of these are as bad as the top 5 though.

• Radar and drain viruses. Way too much power in 1 person's hands given how widespread their effect was and the required hard counter (Expert Hacker, IMO any Hacking cert should've been sufficient).
• The wasp, at least the lockon range (400m? Really?) and the AB duration/top speed (it needs higher top speed and much shorter duration so it can actually intercept things)...
• AI Maxes, although the ScatMAX was by far the worst.
• HA's dominance indoors, more specifically the fact that they're the most damaging and most accurate weapons once you've fired a few rounds or have taken damage. This could be blamed on MA's Max CoF
• The ease with which gens can be taken down.
• Lack of effective air counters for infantry. Cerbs, ESAV, jammers, flaklets were all just weak enough that a skilled/determined pilot could basically farm infantry with impunity. Air Jammers + killing a Mossie in 2 phoenix or 5 striker/lancer shots would've gone a loooooong way.
• Giving one empire most of the 0s0k weapons and the best equipment for CQC where all the objectives are
• boomers
• The maelstrom
• The current lasher