These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anticlimax Boss: The final battle in DM-HyperBlast2 becomes really easy, unlike in the first installment, since the player can get frags by pushing his/her enemies to the void. Plus, the match has a time limit of 20 minutes to win, and it's possible to win via timeout.
Ensemble Darkhorse: The Gen Mo'Kai. The race is just next to the Skaarj in terms of non-human characters' popularity.
Game Breaker: Manta Running glitch in Vehicle CTF mode. It makes use of a non-intended "feature" in the namesake one-person vehicle to carry several players/bots in its wings. Thanks to this, it's possible to do faster flag captures. Made even worse when coupling this with the wing raiders being able to use the Link Gun to heal the vehicle.
A bug while playing with the "Weapon Stay" option disabled allows to keep a Charged Attack (BioRifle's and Rocket Launcher's alt. fires, Shield Gun's primary fire) while picking up another weapon instantly. Your actual weapon changes to the picked one, and when you switch back, you fire the Charged Attack.
Harsher in Hindsight: In the canonized map AS-BP2-Jumpship, you'll lead an Izanagi team who hijacks a Liandri jumpship in order to enter any space they want without a jumpgate. The Bonus Pack 2 was released in 2005. Fast-forward two years later, and an Izanagi team, the Ronin, hijacks a spaceship and uses a jump portal to enter Necris territory.
Due to your teammates being incredibly stupid and the fact you can't be everywhere at once, any CTF level in single player quickly becomes an irritating hassle.
The fourth level of the single player, DM-1on1-Desolation is played with 5 bots. The level is very intrincate, with lots of things in your way such as pillars, narrow passages (which makes them as frag bait when someone shoots with splash damage weapons like the Flak Cannon, the Rocket Launcher or the BioRifle) extremely few options to trickjump, as the name implies it's really small, and the only way to get some armor is by using the Booster adrenaline combo with enough health. There's also an UDamage, which the bots will steal if you don't know how to time it well. Oh, and if that wasn't enough, the bots have a tendency of annoying you unless you react quickly.
Vindicated by History: Unreal Tournament 2003. In it's release moment, it was heavily bashed for having plastic graphics and for "not being Unreal Tournament enough". But nowadays, a lot of people are looking at 2003 with better eyes. Sadly, there're no master servers for the game. (All of these went to 2004)