Great versatile amp
From high gain to clean, and from vintage to modern. This amp's got it all. It has 12 preset amp models (from "clean" to "insane"), a nice digital reverb to give some extra body to your tones, and it has a delay, sweep echo, tape echo (all adjustable with tap tempo), chorus/flanger, phaser, and tremolo effect. It also has 4 channels which allow you to save your favorite settings and a built in tuner. These are easily accessible by the Line 6 footswitches (these also come with an expression pedal!).
All the above makes this a very, very, very versatile amp. I'd highly recommend this amp for beginning players or guitar players in cover bands (although the spider II is a little outdated, Line 6 still makes newer versions of this amp). This amp has so many settings which allow you to explore all of your potential on every musical style. Also, this amp has more than enough power to gig with any band.
Overall a great amp. The only thing it's missing in my opinion is tubes. But that's where the Line 6 amps with Bogner tubes come in ;)
Powerful, cheap amp
My brother bought this amp about 5 years ago 2nd hand for £60, which is a very decent price. Like most line 6 amps, it comes with multiple effects and pre-sets. I usually find pre-sets a bit irritating, as I can't get to know the amp myself, it's like the amp would be telling me what is best. The Line 6 Spider II does this, however some of the sounds it gives off are perfect. I've used this amp for many of gigs (I have the 75watt version) and it's coped well. The only problem I've had is that the nut for the jack input will sometimes unscrew, letting the input go inside of the head, which is quite a pain.