I've logged about 20 hours into the game since launch, and am about to fight Koga for my 5th gym badge. I was kind of ambivalent about the game pre-launch, but I would have to say I've enjoyed it immensely so far, bar a couple of complaints.
Pros:
- 3D environments and characters look great - love details like the oddish-shaped potted plant and the character designs have been translated to 3D really well
- I love the expanded elements of world building, with different characters appearing to supplement the plot, although it does feel ridiculously hand-hold-y at times, especially how you get the tea and the gold teeth.
- Building on that, new gameplay sections, such as a thing which happens in the Rocket's Celadon Hideout, really highlight how video games have expanded even since FRLG in 2004, it's good to see GameFreak not sticking rigidly to the contents of the older games with no attempt to change things around
- Even super-low encounter rate Pokemon are relatively easy to find (unless you want good IVs/natures), so no more spending an hour or more hunting for a single Abra
- Some trainers are surprisingly powerful, like the gamblers and some of the ace trainers
- Progression through the game feels super fast, probably due to the removal of random encounters
Cons:
- Maybe I just didn't catch anything for a while, but there's a bit of a level spike around Celadon/the Rockets/Fuchsia where every trainer's pokemon is suddenly the best part of lv40? Also, because everyone's Pokemon learn powerful moves early due to the massively revised move pools, training lower level pokemon through battle becomes an immense pain
- No held items or abilities really hurts some pokemon (although I can finally spam ground moves on the hundreds of Weezing that are in the latter half of Kanto)
- Catching can be super inconsistent and aiming is sometimes really finicky
- Feels like there are optimisation problems - the game hangs for several seconds when entering/exiting some buildings and stops to think a lot between turns in battle
- Running is too slow, I keep trying to press B to go faster, and a lot of the ride pokemon are so large they bounce of obstacles all the time and constantly despawn
The only really big problem I have with LGP is that ultimately, regular trainer battles feel pointless. They give so little EXP versus chain catching that they're near useless for levelling team members and just feel really unsatisfying. If I didn't constantly need money for healing items and balls I would actually be dodging trainers, especially on the interminably long routes to Fuchsia (although that's a problem that's always been in the Kanto games)
Aside from that, though, I'm really enjoying the game so far, despite having recently replayed both FireRed and LeafGreen. This feels like a fresher, faster Kanto, and it really benefits from infinite TMs and the removal of HM moves, which are probably the best changes from recent generations. I wanted to add more specific Pros, but a lot of them are spoilers.