Not solo friendly? Sure groups are faster but I'm doing the whole Sorc ride solo. 53 now. T3 content is fine solo.
Firewall build was okay for leveling... but now... its absolutely crazy. I've never been playing a more tanky Sorc and the interaction within the build's perks is great (procs!). There is definitely more to D4 than there was to D3. Also the Paragon system is pure stat goodness. They've struck a really good middle ground there, up to 50 there is a substantial difference in the gameplay/build options compared to past it, going from simple-ish to pretty deep.
@Sithaer I concede this point now
Additionally the way the world is integral to the levelling experience with all those Altars you have to find.. yep. Nice. As a result of that and the renown system there is a lot to do even past 50, and it will still just be world exploration and casual mob slaughter. The game is paced pretty nicely at that point. You really haven't played it proper until you've had some time in T3 imho, that's when all things go where they need to go; the game's pace picks up tremendously as does the difficulty, mob density, etc.