The last game I bought was a bundle pack of 5 PS2 games for £10, since I'm still playing my PS2 on account of having no PS3.
In the bundle was:
Sly 2: Band of Thieves: If you're a platformer lover, Buy It. It's far too much fun, and is certainly challenging as the game progresses. As a number, I'd say around 8, maybe 9.
Valkyria Profile 2: Silmeria: I didn't like this. I'm an RPG fan, and I admit that there's nothing wrong with change, but I just couldn't get into the game. Only the graphics impressed me, and that's not enough for me to warrant a recommendation. I'm going to refrain from giving the game a number rating as I confess that I sold it pretty soon after trying it, and didn't finish the game, so any rating would be a bit pointless.
Just Cause: Awful. Pure garbage in every sense of the word. So what if there's a massive map to traverse and multiple ways to do so if the gameplay is so bad? Avoid, avoid, avoid. I'd give it around 2, possibly 1 1/2, but that's being generous, methinks.
God Hand: Lots o' fun. Much like Devil May Cry, its not just an out-and-out brawler - you need to get into a rhythm of dodging, fighting back and using the special moves. The game also gets points for featuring a special move where your character kicks his enemy in the testicles, causing them to collapse, their face turning purple with lack of air. Very difficult, but satisfying. 7.
Viewtiful Joe: A brilliant game. Fun combat, awesome visuals, great sounds, and some fantastic set-pieces, such as making a bus fly through the air via use of slow-motion effects. The game makes very little sense, but it far too much fun to criticise. Another game which is difficult, but once you get into a pattern, you can do it. 8 or 9.