The biggest change AFAIK is the journal. Now you can access your active quests which are shown in a list (though it's a little off, some in my list are ones I've completed properly) instead of everything listed alphabetically with cryptic names. Which is reason enough to make the change sooner rather than later! There are quests in my list that I forgot I ever had because of the jumble in my journal!
As far as other things go, it is no slower, if anything I find it a bit smoother (though I've only played with Tribunal twice, so that may have happened anyway). I'm not sure what changes the tribunal patch makes to things like levelling up though.
There are a couple of other helpful additions as well like being able to make notes on your map and hire a mercenary or pack animal (unclear how helpful these last two are though
). Basic stuff like combat etc don't change.