It's basically described well by Alex and Thomas, but I'd like to restate that it's much more feature-paked than any Canon remote for cameras without the "N" fitting or whatever it is.
I think Thomas either got a different item to me or ot it slightly wrong, the "number of shots" can be set up to 399, not 99, but to be honest you'll probably either use infinite or <99 anyway.
Now on to the bad points: it's a little cheap (quality-wise). The timer can hop around a bit in how long it thinks a second is - it's hard to represent this textually but it'll do something like:
1---2---3---4---5---6---7---8--- <-- real time
1---2--3----4---5---6----7--8--- <-- how the timer can count sometimes
So it averages out at a (real) second per (its interpretation of a) second, but if you need it to be precise, then it may disappoint.
Luckily, I'm using it for time lapse, where the camera will decide the shot length and the remote is used purely as an intervalometer with large enough interval for the odd second not to be a problem, and astrophotography where the shot length is generally long enough not to be affected by this.
Also, one thing that kinda bugs me about this but it's not a problem is that it's always on. The only way to turn it off is to take the battery out. Having said that, the manual specifically states that it's an always-on device (like a watch!) so I guess that's normal. And it doesn't seem to be using a lot of juice, although I wouldn't know as I've only had it a couple of weeks (but the battery hasn't died yet!)
And yes, the cable is somewhat short but not really a problem for me.
Hope this helps someone out.