[vicky_molokh]

Originally Posted by Ultraviolet

But also offers more in the way of tactical choices and finesses...which also translates into "lots of difficult and time consuming rules"

A standard resolution of an attack is thus:

1. Roll to hit (with modifiers if appropriate)
2. Target rolls defence (if can defend)
3. Roll and apply damage (for some attacks, this is replaced by a Resistance roll against a non-damaging effect).

GURPS adds the second roll of defence most of the time, this is true. However, everything else has mostly the same building blocks as in D&D.

What accounts for longer turn resolution is primarily people (especially newer players) spending time considering the possible options. Since newer players are more likely to post their first impressions, the reputation of a slow system crops up.

So why the long consideration? Well, in D&D, many options become available with Feats (e.g. called shots to the leg). In GURPS, most such options are part of the skill; if you know Staff, you can use it to Sweep enemies; it's just that being trained in Sweep makes it significantly easier to do than if you 'merely' know the general Staff skill. All that means that whether to use a particular 'feat' depends on the situation (you can check out the recent Guide to Tanking for examples of situational Techniques).

Another interesting note is that, at least in my experience based on gaming D&D/D20, a successful attack in GURPS is likely to have more an effect than one in D&D. This is because GURPS doesn't have such a significant increase in HP as characters gain experience (in realistic games, anyway; in Supers and the like you can expect more HP).
So while getting 3d6 damage past Damage Reduction in D&D is no big deal against a veteran Fighter (easily 15d10 HP total, right?). Getting 3d6 damage past Damage Resistance in GURPS against a veteran 'fighter' is pretty brutal, and can often be a fight-ender. (Of course, there's the issue of getting past defences/armour, but I'm trying not to overcomplicate things.)