Struggling to think of any game sequel that was built by a different company than the original, that didn't turn out to be a pile of horse shit. Examples are welcome, because I would so love to discover some reasons to look forward to this!
Dota 2
Wat? DotA 2 was handled by IceFrog under Valve. IceFrog made DotA: Allstars. Before then, yeah, DotA changed hands a bunch, but going from DotA: Allstars (the absolutely most popular version that got everyone's attention) to DotA 2 was not handled by anyone different.
As for sequels made by different companies...
Wasn't NWN and NWN 2 handled by different people, and isn't there a divide in which is considered the better?
There's also Matrix's acquisition of the rights to the Close Combat series, which it re-released and then produced full releases of.
Tropico 4 is considered a pretty good game, although Tropico 3 was a bit jarring, Tropico 2 was made by the original team and not considered that good and Tropico 1 was a classic. That said, Kalypso doesn't have a perfect track record (Looking at you, Patrician IV and Port Royale 3...).
On the topic of Tropico, PopTop Games, the developer for Tropico, first came out with Railroad Tycoon 2, which is also considered to be a classic, though they were not responsible for Railroad Tycoon 1.
Hmmmmm...
Hi-Rez and Tribes: Ascend from the Tribes franchise...
I got nothing after that.