The UnderGarden is a slow casual experience with beautiful visuals and relaxing music. Good for that slow lazy evening yet offers a bit of a challenge if going for gold.
Think Creavures, Aquaria, even Sparkle 2 Evo - a slower-paced adventure with a heavy focus on mesmerising visuals and a soothing soundtrack. The aim of the game is to pollenize the underwater flora and explore the levels for secrets. There's no need to rush so it's perfectly fine to just relax and take time solving the odd puzzle. For those more interested in score it's certainly possible to go for speed as each level is scored and time is recorded. Something to appeal to both casual and core gamers.
The puzzle design is not ground-breaking but does what it has to do without compromising the relaxing nature of the game too much. There are lever puzzles, push-buttons that have to be held down (or up!) by special seeds, and some other physics-based puzzles. Some puzzles have alternative, less obvious solutions that lead to secrets and bonus collectibles so it's certainly worth the while to experiment a little and try to explore every nook and cranny.
I suppose I would recommend the game to anyone looking for a decent time without the fast pace of more modern games. It's not often that I play casual games like this, but the visuals and an overall calm atmosphere are hard to pass up.