pi4t: Well, in this case the vast majority of the content it adds is taken from the tabletop version of the game, rather than being created by the makers of the PRC. Of course, that doesn't mean it doesn't contain some content which is more powerful than others - dnd 3.5 is known for some options being significantly more powerful than others - but it helps to limit it. And they don't just include the most powerful options from 3.5; there's a variety of classes of different power levels, even down to the infamously rubbish Truenamer.
So yes, there are powerful options added, although possibly not too much more powerful than the vanilla wizard (considered one of the most powerful and flexible classes in pnp; it loses some flexibility in nwn because of engine limitations, but can rest and switch out spells far more often than you reasonably can in pnp). On the other hand, there are also new options at all the other power levels, so you can pick something suitable for the game you want to play.
The PnP game has the discretion of the DM to keep things from getting out of hand.
PRC has ridiculously overpowered content that will essentially eliminate the challenge of most modules.
The OP was asking about races. Here are some PRC examples:
DragonKin:
Dragonkin Ability Adjustments:
+8 Str, +2 Dex, +2 Con, +4 Wis, +2 Cha - Darkvision: Allows them to see farther in the dark.
- Natural Armor Bonus:
Racial natural armor bonus of 7.
- Natural Weapon: Can make natural claw attacks(1d6 each).
- Dive: +2 attack while suffering -2 to armor class. A successful attack does double damage if using a piercing weapon.[/i]
Troll:
Troll Ability Adjustments:
+12 Str, +4 Dex, +12 Con, -4 Int, -4 Cha, -2 Wis. Natural Armor Bonus: Racial
natural armor bonus of 5. - Regeneration: Innate ability to
regenerate 5 hit points per round.
Compare with the strongest race in the standard game. The Half-Orc:
Orcish Ability Adjustments: +2 Str, -2 Int, -2 Cha. The Dragonkin/Troll and countless others are completely unbalanced. You may as well just
turn on God Mode.
On the race front at least, effort was made to balance the original game.