I've been playing quite a few platform games of assorted different stripes recently. Thus, I've had a chance to realise what kinds of thing I like and dislike, by seeing assorted different takes on the genre.

Cave Story

Thanks to l_the_fangirl, I went and downloaded Cave Story and its English translation patch.
What's good: The plot is impressive, if rather bleak. The difficulty level scales pretty smoothly. There are lots of different weapons, each of which is useful in different circumstances. And the plot branches and the game has several endings.
What's not: The game apparently has lots of secrets, but they don't seem to be the kind of secrets I'm good at finding. (By comparison, I found every secret coin and star in Super Mario 63 below.) I found a number of difficult-to-access regions, but the rewards were minimal to nothing: mostly empty rooms or strange creatures who won't talk to you. Also, for a MetroidVania which is hyped for nonlinearity, it seems pretty linear.
Rating: I think I'd need to play it through a couple more times to be able to say.

Super Mario 63

An Flash game which makes unlicensed and thus illegal use of lots of Mario graphics and sounds from his assorted 2D incarnations. Play it online here.
What's good: Highly nonlinear: there are 64 stars and 64 coins to collect, spread through 12 worlds and the castle, and you can do them in whatever order you like. The gameplay is classic Mario in the best way, with the FLUDD from Mario Sunshine back-ported to 2D style. The level names and themes are mostly homages to levels from Mario 64, but the puzzles and specific level designs are new.
And the game's absolutely brimming with secrets, from obvious ones to really tricky and subtle ones. The difficulty curve is great as well: by world 3 things are getting a little tricky, Bowser's worlds are nasty, but the fun-to-frustration balance is very nicely done. (Okay, apart from the route to the very final star, which took me 50+ lives to beat. But that was a fitting conclusion to an excellent game.)
What's not: Not much to say here. The bonus for getting all 64 coins would have been rather more useful at 63. There are one or two glitches, but they're extremely rare.
Rating: Almost full.

Knytt

Found this one following a link from Vitenka on the ToothyWiki FreeGames page. It's a big explore-the-map affair.
What's good: The regions of the map are pleasingly diverse. And the map is pretty big.
What's not: There's nothing to do. Really. The only tasks are explore and collect 20 items, which do nothing. Which is fine as far as it goes, but... I'd much prefer it if those items did something, or if any of the people you find could be interacted with, or if there was any kind of plot, or... I thought I liked exploration games, but it seems this game is too pure exploration even for me. The map is very large, but there's nothing to stop you going straight from one end to the other: no regions inaccessible without a given item, no jump upgrades, not even any doors and keys.
Rating: Quarter-jump.

An Untitled Story

Another link from Vitenka on the FreeGames page, but this one's a lot more to my taste.
What's good: This game has properly nonlinearity: there'll be at least 3 or 4 open areas at any given time, and if you find one of them too tricky, you can easily head off to try a different one and maybe get a couple more powerups to help you in that one. The characters actually talk (once you get the right powerup), the regions have names and distinct flavour, and there are a huge number of powerups, most of which open up either new areas, or new sections of old areas. The bosses are tricky, often taking 2-5 tries but rarely more than 10, which feels about right to me. The automap shows your percentage completion of the whole thing, and lets you warp between save points (once you get the right powerup), which is an excellent feature. There's a nice helping of secrets and rewards for doing certain sections flawlessly. And everything just flows smoothly: it's quick to teleport around to the areas you want to try, it's quick to restart when you die, and the game gets out of your way and lets you get on with playing it.
What's not: The graphics seem pretty MS Paint-y, particularly at first. There's not much of a plot.
Rating: 880.

Eversion

"A cute platformer with a dark secret".
What's good: I really like games which have multiple versions of the same level, each of which behaves subtly differently. This is the central conceit of this game, and it does it well. The spoof of the happy platform game is funny, and it gets nicely creepy as the game goes on. The final level is a puzzle masterpiece of weaving the seven different depths together.
What's not: It's basically a light piece of Lovecraftian fluff (and there's a sentence I've never written before). Don't expect too much.
Rating: Three tentacles.

GENERIC

Here.
What's good: It's a comedy tweak of the platform game with a very interesting twist. Most levels are pretty easy to reach the end, but most of them are startlingly difficulty to get every treasure.
What's not: Like Eversion, it's just a simple fluffy free game; don't expect too much.
Rating: ZZA

Portal

Well, I have been playing Portal as well, and it is clearly a platform game. But it's not free (although thanks to a link from robhu I got it for £3), it's 3D, and it's generally sufficiently different to the others above (and probably doesn't count as "indie" any more either) that I'm not going to try to compare it. Nonetheless, it's very cool, and I love the sense of humour. "The Enrichment Centre would like to remind you that the Weighted Companion Cube will never threaten to stab you, and in fact, cannot speak. In the event that the Companion Cube does speak, the Enrichment Centre urges you to disregard its advice."
Rating: 83 mph.


Does anyone have any recommendations of other games I should try? I'm probably planning to try Braid at some point soon.