Is it weird I like the Christmas Special more than the main game?
The main game is a lot. A LOT. The main character Alex (can be renamed with a mod) is... exceedingly unlikeable... on purpose. He's an awful person, and the narrative constantly reminds you of that fact. That's the point. And this awful person gets a LOT of girls. Some have recurring events, some disappear from the narrative entirely. Some areas go underused after the initial exploration push.
The scenes are Honey Select, and most of the girls are designed well. There are a few custom graphics here or there, and they get more common the later in the development cycle the scenes debuted. The girls' personalities are all over the place, which is a benefit. I don't think any girl is particularly well written, but no one feels like a waste of reading time either. The sex scenes get pretty samey because Honey Select, so that's something you should be aware of.
For those of us who like swinging, the Sharing Mode works great. Alex is still the main character getting a ton of sex, but others can join in the fun too. All of those scenes are 100% optional (except MAYBE Shibuya's ending?).
Despite the Completed tag, the game is maybe 95% actually done. The Harem Ending in particular is only partially completed, which is actually ALSO a better gameplay loop than the main game, to the point where the main game feels like an extended intro for this game and it really should be a pseudo-sequel or spun off executable like the Christmas Special. I like what's in that ending and I REALLY want to see more.
On the subject of the Christmas Special, it takes place in the same setting - duh - and stars Milena, one of the many girls in the squad, even requiring some prior knowledge from the game. The game changes from straight sandbox to puzzle solver / exploration sim, however rudimentarily, the story is actually pretty fun, and it made me like Milena a lot more than I did in the main game. Don't worry, NTR Haters, Milena still only fucks one guy, and that guy is still Alex... unless you're on the New Game Plus, where she's allowed to get dirty with some of the other guys or enemies. For a minigame made in only nine days (by the creator's own admission), there is a LOT to like here, and I am very impressed.
All in all the Solvalley experience is a solid one, if you can stand the main character. Very highly recommended for sandbox fans.