NS2 was okay but it cycled rapidly between periods of being amazing and being utter dogshit because of poor balancing and the devs implementing fucktarded ideas without any thought behind it. Such as when they added boneshield regen to onos, which made them able to literally 5v1, but have since removed it but didn't give the onos anything back to compensate, which means now the onos can't even 1v2 marines, even if the marines lack any upgrades or weapons.
Right now pubs (>pubs because comp is equally fucked, screw playing "comp") are entirely decided by lerks - if the aliens have a god tier lerk player that can go 34/2 over a round, they win 70% of the time. If the aliens don't have any good lerks, they lose 70% of the time. The remaining devs - who are actually just "community members" that do it for free - have such a fucking hard on for them and buff them every few months despite them already being the best lifeform.
There's also the huge gap in skill between people who know what the fuck to do, and others that treat the game like a team deathmatch. Unfortunately most people that get drawn into the game by free weekends are mouthbreathing tards who just got out of CoD, and they leave after two rounds of pissing off everyone on their team.
NS2 had potential, and they even (mostly) fixed the performance issues after several years, but they cater too much to their "pro" players despite the fact that all the pros already use a competitive mod that already diverges from the main game. Most of the bad changes to the core game can be attributed to them.