Go for it!
I recently went the opposite direction and bought a 360 to catch up on exclusives I've missed (primarily Trials Evo and Bayonetta*), but if I'm honest, the backlog that's resulted from picking up loads of 360 titles on the cheap means I'm probably set for at least a year into the new gen!
You could probably have the Uncharted trilogy for about 25 quid, 3D Dot GAme Heroes is worth a go, Valkyria Chronicles, Wipeout HD, etc. Tonnes of content with them. There's also a smattering of HD collections to be had!
On the whole I'd probably say I prefer Dark Souls to Demon's, but it's still one of this gen's must play games.
So erm, yeah, don't buy a PS3!
*I know it's a multiplat, but the PS3 port is so bad it may as well be an Xbox exclusive
#9567428, By Demon's Souls