Trine 1 and 2 are fantastic casual action platforming games - possibly some of the best in the puzzle platforming genre. Trine 3 tried to fix what wasn't broke, in that it went from 2D to 3D - development expenses reportedly ran out of control and we ended up with a lack lustre product that wasn't fun and is hard to recommend.
Thankfully Trine 4 has gone back to its roots. It's just more Trine (a lot more - this is not a short game) which is not at all a bad thing. Excellent, cheerful, very colourful graphics, (indeed these are arguably the best graphics of any 2019 release so far imo), tight controls, plenty of scenery variety and with multiple ways to solve many of the puzzles. The only slight negative is the combat sections which are too numerous and get somewhat repetitive (fortunately they are never particularly difficult). The story is also not fantastic, but it serves its purpose for the crew to get back together.
Trine 4 delivers exactly what you'd expect from Trine. If you have not played the earlier games, it doesn't really matter story-wise, but I would urge anyone interested in this game to play the original two games anyway (but skip Trine 3 - it's just not "Trine").