Both Shadow Complex and Trials HD are worth their $$$. IMHO, knowing just how awesome Trials HD is, I would not have hesited to pay $50 for that game.
Difficulty level after medium: I hear you, I've not completed the hard levels yet but I can provide a hint though: check out the leaderboards for those tough levels and check out the top player's instant replays. That's how I started getting better. Even if the game is kicking ---my bottom---, it's the main reason why I love it: old school gameplay that's hard and rewards skill. When you finally finish one of the hard levels, it's quite rewarding.