Game type: browser-based, life sim, "MMORPG" (vaguely)
Time demand: It may just eat your soul, be warned! Although in theory, however much you want to put into it.
What it is: Yes, I put MMORPG in scare quotes up there, because it sorta is, but not really. For one thing, the graphics are a lot more basic.
Anyhow, this game is put together by just a couple guys for the love of the thing, and considering that fact, it's damn impressive and immersive. You start out with a character (only one avatar for male, one for female, alas), pick a name, get a few very basic supplies (torches, a bit of food, and some basic clothes), choose to spawn in either a handy village or the middle of the wilderness, and *boom* there you go, now you gotta make your way in the world.
And this world is... not always easy to make your way in! Especially when you're still learning your way around. For instance, nearly everything you do takes up some of your stamina bar, and as your stamina bar recharges it lowers your fullness meter, which means that while you're going around doing stuff, you need to eat fairly frequently. Which is okay while you have the four or five bread you start with, but after that you need to find your own stuff, which can be tricky.
Then of course there's the fact that some animals are aggressive (bears and boars) and might kill you if you come within range of them, or might just knock you out. It's a toss-up. And when your character actually *dies* (due to damage, starvation, drowning, what have you), they die. You can start a new character and "inherit" (spawn back at previous character's spot, inherit some of the points you'd earned and put into your previous character, etc.), but it's a new character, and definitely a setback.
And mention of the points you earned brings me to that topic. You start out with a 10 in each basic attribute, and 1 in various overall skill categories (such as farming, exploration, cooking, etc.), and ideally you want to raise those in order to perform various tasks well, make good quality items, and so on. Attributes are raised by eating certain foods, bit by bit, while you can raise skill categories by spending LP, which you gain by... well, doing pretty much anything in the game. The tricky part is that LP is also used for buying your actual skills which let you build and craft things, hunt, farm, and so on, as well as for claiming land for your very own. So you get to choose how to spend them, and it can be... overwhelming.
While you start out only doing very basic stuff and it doesn't seem very impressive, you can eventually build your character up quite nicely, and make yourself a very nice habitation, clothes, so on and so forth. You can even tame certain animals which then become domesticated versions that you can use for their produce. (Aurochsen, for example, become cows and give milk.)
The main downer for this game (for me, and for many players probably) is that it's an "anything goes" type of game. Which means that there is inter-player combat, experienced jerks may come along and kill you, loot your stuff, whatever, and it can be a while before you get built up enough to defend yourself/build defensive structures, which makes it a matter of luck as well as skill to keep from losing your progress in various ways, just due to the fact that you share the game world with creeps (as well as good people). This can be very disheartening, to say the least, although you could also consider it an added challenge as well. On the bright side, the world map is enormous, so if you spawn out in the wilderness (or move away from your starting area before settling down) chances are you can end up someplace more remote, where people aren't as likely to find/bother you.
Adding to the challenge is the fact that the game has a wide player range, with many Americans playing, but also many Brits, Russians, and so on, so any random person you run into may or may not even speak your language, so.. pretty much any person-to-person encounter is going to be an entire toss-up.
All that said, it may not sound like an appealing game, but something about building your little character up slowly, unlocking more and more skills, buildings, crafts... it's just neat as hell! So if you like sim games, sandbox type games, or just anything of the sort, you might want to give this a try, and see if the pluses outweigh the minuses for you.