I use the n52, and I just got the nostromo off of Woot a bit ago. I swear by it. I use it in FPS (BF2142, Section 8, Killing Floor, Borderlands, Arma 2, Payday, Sniper Elite, BFBC2/Vietnam) and MMOs, and other games. In every game, it takes my hand off of the keyboard and puts the commands in a small area. The only thing I don't like is that it doesn't have enough (or dedicated) keys for the shifts, so you have to take a key away in order to get access to the other magnitudes of keys. I have a G13 also, and though I love the fact that it has more keys, the n52/Nostromo fits the hand better- the G13 is truly a small keyboard, and so takes more retraining.
But get a nostromo and a programmable mouse (I have a naga, though I think if I had it to do over again, I'd get a Hex), and take a bit to learn what your patterns are in the way of controls that you use, and don't be afraid to tweak. It might not make you better, but it will make your experience better.