It's not so much that it was extremely easy (as in not a single fight was challenging at all), but the opponents didn't use any tactics.
At least Malak did some running around to heal himself and power up. The downside was that it gave me time to heal, though. But in KotOR II the bosses didn't "do" anything. So you could just hit them over and over.
Compared to other RPGs, this is rather disappointing. Like in Baldur's Gate, Sarevok had all kinds of minions - which made it a difficult fight. In BG2 you had to hack through alot of protective spells to even be able to hurt the boss. In ToB you had the minions, boss retreat, more minions, boss retreat etc. Even if you slaughter the boss, the fight will still be drawn out because of the "tactics". IWD also had the minions, retreat, more minions, traps, retreat thing. Same with NWN:HotU.
Even if Nihilus was easy, I would prefer it if he had an unstopable uber force push to send you to the other end of the bridge whenever he needed to heal or buff. And if you weren't careful he could uber force push you into open space. Oh, and since he could stun you all without a save, he should just keep your weaker companions stunned throughout the whole fight.
I don't like just giving the boss twice your AB, Defense, HP, and saves - but give them a tactic to draw the fight out. What I prefer is a very high difficulty level on boss fights, though. I mean... it's a singleplayer game, you have quicksave/quickload. Make the fight so difficult you have to quickload a few times before you figure out how to beat him. Like in Hordes of the Underdark my wizard didn't even have any spells prepare that could actually hurt the end boss. So I had to try a few times before I could take him down. Like it should be in my book, yo!
And to not sound too negative... I liked the game alot (while not extremely satisfied with the half-finished ending), and found the roleplaying part challenging and fun. But not a single fight with my main character was challenging.