Time4Tea: I'd say many RPGs might fall into that category of improving in the second half. At least, they
should, since your character is developing, gaining new skills and abilities, so the back half of the game should be more interesting. However, I think the challenge with RPGs is in maintaining quality of content over a long game that might last 50+ hours.
Especially D&D-based RPGs that start at level 1 are good candidates, since often in D&D the first 3-4 levels are notoriously dicey and you tend to always face the same small and predictable selection of enemies (goblins, kobolds, giant spiders ...). So, I'd put forward Icewind Dale and Baldur's Gate 1, since they are low-level D&D campaigns that maintain a strong level of quality through the game.
I was going to suggest games that have an inverted difficulty curve, since they can be brutally hard at the start. Although, they are often far too easy in the late-game, which I'm not sure is necessarily better!
Problem with RPGs is that, too often, they have an inverted difficulty curve.
The way I see it, an RPG should steadily increase in difficulty (possible temporary exceptions, like after the party defeats a major boss (like one with major plot significance, if the game decides to go the plot route, or one that opens up a major part of the world to exploration), so that the player has to actually use those new abilities they've been gaining over the course of the game. The game should start easy, so the player can get past the beginning of the game where options are limited, and then increase the difficulty once the player is given the tools to overcome it.
Icewind Dale does something that Baldur's Gate doesn't; in the starting town, before you have any real combats, you can do side-quests to level your party up from 1 to 2, mitigating the issue that AD&D combat is terrible at low levels.
On the other hand, there's the occasional game that's a bit too backloaded, with many interesting abilities and/or items not appearing until rather late; in the SaGa 3 remake, something like half the weapons are all in the endgame section (once you can fly over water in the alternate dimension). (This is in contrast to SaGa 2, where you actually get most of your endgame equipment some time before the endgame.)
(Worth noting that this idea can be applied to any game where the player gets more options as the game progresses, including games like Zelda-likes or Metroidvanias (Castlevania: Symphony of the Night being one example of a game with an inverted difficulty curve here).)
StingingVelvet: Maybe they spam you with endless enemies, maybe the story gets over done, maybe the game just drags on too long.
Or maybe the game gets so easy that it feels pointless, and isn't allowing you to really make use of what you've learned through playing through the earlier sections.