I enjoyed the first one as much as this one, which surprised me since I went in knowing that it wasn't going to be the same genre as the first (since the writers mentioned that they wanted to make each film a different genre), so I wasn't expecting to really enjoy the sci-fi comedy spin they put on it, but I did. They've answered questions left over in Happy Death Day without crowding it in and neglecting the plot of Happy Death Day 2U. They've also made it different enough from the first film that although I thought I knew what to expect going in, I was wrong and in a good way. I wasn't confused by anything that happened, which sometimes happens when sequel films try to make things too different from their predecessor, but HDD2U handled it perfectly.
There's a set-up for a possible third film in the franchise, and given how much HDD2U impressed me I'll definitely go and see any future third film that's created and look forward to it.