Depends on how you see it. As a (primary) phone, it's relatively slow and has some really unexpected quirks. I come from S60 (non-touch) and have never started to use the N900 as my main phone. The old Symbian device from 2007 performs a lot better, can do all the "phone-stuff" the N900 will never be able to do and has a much better battery life.

Still I have the N900 with me most of the time (2nd SIM card, same number), and as a computer, it's powerful, fast, flexible, open and still keeps amazing me after almost 1 year. It's faster than 2 of the PCs I regularly work with, it has better battery life and connectivity than my laptop and it integrates perfectly with the rest of my network. (I run GNU/Linux exclusively.)

So as many others said before: Do you want a stable, fast phone full of features? You'll find a better one. Do you want a damn sexy and fascinating, fast, always connected hybrid computer/phone-gadget? There's nothing that could beat the N900.

Oh, btw: Why not buy the N8 now, wait how it evolves (there'll be a new firmware for it, too, don't forget).... and then sell it and get the N9 we're all waiting for?