Just finished Serious Sam 2 for the first time, it was fun, but some of the boss were just annoying to fight, but I can't put my finger on why. Some of the phase in vehicles were good, others not so much.
The problem isn't always due to the end bosses, but due to the fundamental differences between SSam 2 and... all the other SSam games. I could spend all day going through those, so let's just try to stay on topic here.
The first boss fight (giant gorilla) looks awesome at first, but then you spend the fight killing mooks so that others can kill the boss. Pretty anti-climatic.
The second boss fight (giant
wasp cunt with wings) revolves around destroying the recharge stations before taking on the boss itself. A rather tired mechanic, especially since SSam: SE did it already, and even with an insect-themed boss!
The third boss fight (oversized sumo fighter) is actually decent for a SSam game. The destruction of all the scenery as he stomps about adds a nice touch.
The fourth boss (Kleerofski) was annoying, not just because it is based on the same mechanic as the second boss fight, but also because of the whole "Planet Kleer" thing where the most annoying SSam enemy gets the spotlight.
The fifth boss fight (dragon) is probably the worst one of them all. You have to gather ammo for the One Weapon that hurts the boss, while also doing platforming stunts to reach both the ammo and the One Weapon. Repeat as needed. Yawn.
The sixth boss fight (giant robot) is the same as the fifth, except this time you first get the weapon, then the ammo. Otherwise it's the exact same thing. Double yawn.
The final boss (giant fucking pyramid) has a glaring flaw that left me with a bitter taste in my mouth: During the fights leading up to the boss you get a hovertank vehicle. It does X damage and is pretty neat to have. BUT, once the actual fight against the end boss begins, another vehicle is presented (it even looks the same as the original). What the game does
not tell you at any point is that this second vehicle does 4X damage, not just X damage. Meaning, that if you were skilled enough to last up until this point with the original vehicle, you will not want to get rid of it, even when another vehicle is presented. Well... that's precisely what the game wants you to do. Get rid of the first vehicle, and hop on the second one.
Now compare it to the known bosses of the other Serious Sam games:
With the exception of Ugh-Zan III needing to be 'damage-stunned' to be finished off, there were no gimmicks involved in SSam FE. He was big, he was bad, he had Really Big Guns. Take your Big Guns and fire them at the Big Bad until it dies.
The bosses of SSam SE were overall pretty fair, even though they tried to introduce their respective themes. The end boss was a bit of a dick as his gimmick was pretty old, but still nothing to complain about, really.
The bosses of SSam 3: BFE were a little gimmicky (especially the end boss) but nowhere near the scale of SSam 2's bosses.
Bottom line: There are a lot of reasons to hate on SSam 2, and they all have to do with the overall tone of the game, not just the end bosses.