Nothing like the sound of a true tube amp. However, the thing thing them is that they need to be cranked n order to get the effect to the fullest, try cranking a 100w Marshall JCM head with decent tower and try to play...amazing...but f'in LOUD.
Since I play in my house i have a smallish marshal 30w which is fully digital but comes with FDD (frequency dependant dampening IIRC), which like frothy said is an algorithm used to achieve a nice tube sound. TBH at normal levels I would be hard pressed to find a difference between it and a tubed one. This is why I prefer my current digital amp to a tube one, this is just my opinion based on my situation, if I was playing in a band or was in a situation where I needed something louder a tube would be the only thing on my mind.