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Second life is the vacuum tube of player-content-virtual-worlds. It's not worth recommending to your RL friends, and in most cases Internet friends. The only possible exception would be if they really really like making stuff like I do.
The only reason Second Life will be competitive for the next few years is because they're man-decades(like man hours) ahead of any competition, and what could be considered a type of achievement entrapment(I already play this game why move). They really only need a competent developer to put major time into a game like Second Life it to start bleeding users.
The only thing that Second Life is good for is proving that there is a wave for this exact genre. But they're just the wave that you'll surf on till the real one comes along.
The only thing the game has going for it is that it's an awesome building platform, people have litterally made their own mini-MMO's which are focused on roleplaying. From the building you get a decent socialization game, whether it's in themed SIMs or just talking to people while you work. After that Second Life has very little to offer, even though there is a lot of stuff to see and do because of the stuff people have done.
In half a day and with the right people you can make a scripted paintball game with capture the flag and be able to enjoy it with some internet buddies for months/years if you wanted to. Granted if you didn't make it yourself you'd probably end up spending atleast $50 for someone else to make it. Such a nice building system and very little moderation also gives you a just like the internet type thing to happen. Just to give you a general idea the lindens(people who run the game) put down about 10% of sales are based off of sex items/similar while 'power users' put that estimate down at around 30%.
As for stability it sucks. There are always a couple of times a month where people on my friends list are crashing and logging back in at about the speed that you'd expect kids to run in and out a screen door. The lindens own stability metrics put 20% of all client exits are actually a crash of some sort or some other failure. You can expect a time or 5 a month where the general population won't be able to use core systems of the game. And just all sorts of junk like that.
As for cost it's possible to play F2P but it'd be annoying to. Most users pay a whole lot of cash to play the game some people have several hundred dollars worth(in some cases much much more) of in game assets. I have about 40 dollars worth of stuff granted I only ever paid 5 into the game to get the payment info used tag and some cash to start uploading stuff, I've also withdrew some money to buy a cheap java programming book since I was quiting for a while. To be honest someone with only programming experience from a few junk highschool classes could end up making a hundred dollars a month after enough time, granted to get that far in most cases you would have to work in SL like a part/full time job and not something I wouldn't bother with after haveing a few commision based stuff out(so you don't need to put money in).
Edit: vacum tube = predcessor to transistor just to clear that up. they weren't bad at the time but once transistors came along and then a bit more developement it was no contest for which was better.
I find it amazing that by 2020 first world countries will be competing to get immigrants.