Solasta's UI feels net superior, snappy, intuitive, and very responsive during fights. Same with the camera. The movement squares are helpful for proper positioning, especially in hard fights.
BG3 lags behind in this by quite a lot, more obviously in fights spread across multiple elevations (say mob1 is at 5, Tav at 8, Shadowheart and mob2 at 12, mob3 at 15, etc). The UI feels cluttered & has to be reorganized for every character, every new playthrough. The camera movement can get buggy, as others have mentioned, randomly jumping elevations or not focusing properly.
Both games have some nice environments & some that feel rushed. Solasta's Dark Castle Cemetery for example, feels very atmospheric but BG3 pulls a bit ahead with the Underdark & the Sunlit Wetlands.
Solasta's characters are hideous. The cinematics are like school-assignments from bored college students. Even at ultra graphics they still look like NWN characters from over a decade ago.
BG3's characters are obviously better looking and better animated - but not necessarily faithful to DnD lore.
Solasta's group ability checks & picking the most proficient character are 2 convenient and fun to play mechanics. Teammates help each-other and it's been implemented in a way that feels natural. Everyone gets to contribute but if you want to roleplay an answer with lower odds of success, you can do that too.
BG3's solo checks are incredibly annoying. Sometimes every team member makes a world check, sometimes just the nearest person. In after-fight dialogues, only the closest person to the NPC talks so you might get stuck with someone who will fail the checks. Not to mention, even if you pick the speaker you want, all your teammates are still near you and don't help which makes no sense knowing how opinionated they all are. (Gale would jump in for History & Arcana, Lae'zel would probably try to Intimidate, Wyll to Persuade, etc)
Solasta's teammates banter but their relationships don't grow in any meaningful way. I still head-cannon the cleric and ranger having a thing (because of how they tend to finish each-other's ideas) and the sorcerer is really sleazy whenever the ranger crawls ahead... he always says smth like: "You look like you've been doing this all your life" "Spent a lot of time on your knees?" Victor, please, for the love Maraike, shut up!
BG3 has that beat because relationships develop: friendship, disdain, hate, or romance. (I'm a sucker for in-game relationships: friendships, rivalries, romance! Garrus and Shepard were best buddies all throughout the trilogy; my Trickster was probably Regill's worst nightmare but he also trusted the commander to the end; Daeran married said Commander and the nobility wanted them as the new king & queen over Galfrey; Alistair married his Warden; Hawke killed her best friend Anders; Solas must have broken the hearts of half a dozen of my Inquisitors; Gann and the Shard-Bearer brought ruin to the world, and so on) In BG3 there's a lot less party banter than in Solasta though, and I think that's such a shame. These people have so much to tell Tav but so little to tell each-other.
Solasta's combat is more fun than BG3's combat (aside from gimmicky builds and cheesing) atm. I hope that changes. BG3 is still in EA, so they can still work on it.
It's not really fair to compare stories since we only have Act 1 of BG3... but even so, BG3's story seems a bit more complex than Solasta's, with many smaller plots weaving into the overarching narrative. We'll see if it develops into something fun & interesting when the full game comes out.
