Hi Mafia Tiger
In answer to your questions.
Vatsim is a network of servers giving (in my opinion) the best 'as real as it gets' flying experience.
It does of course depend on what you want from your flying. Vatsim take it very seriously and people coming online to fool around like on the msn zone will soon get themselves banned.
However if you wish to fly with live ATC from one airport to another, being handed over from ground to tower, getting take off clearance and handed over to approach and then control, getting vectors to your destination until handed over to Approach and tower again to land then this is for you.
Most evenings there are 500 to 600 pilots and atc online making your flying experience realistic and enjoyable.
You will however have to make some effort in knowing Radio procedure and of course how to fly your aircraft and if flying IFR then how to make a flight plan and fly Sids and Stars. But the effort really is worth it and although it may seem a bit much, it makes everybodies time more fun if we all have a basic grasp of the concepts rather than allowing people with no idea how to fly onlne.
However the good news is that its not that hard to learn and there are places that will help you get started.
You will need a proper email address though.
The atc can be by text but is usually by voice. These days the only accepted voice software is AVC (advanced voice client). This is a free download.
To get online can be a little traumatic getting the software working, but once again help is available, and it really is worth the effort.
Soon though Squawkbox 3 is coming out which will make it all that much easier.
By now you may have guessed I am somewhat biased.
Well yes I am I fly for a Virtual Airline and all my flying is on vatsim, unless I am testing something new. And I no longer consider it flying unless I am on Vatsim.
Alternatives?
Well in my honest opinion there is only one other organisation worth considering and that is IVAO.
They are a little more relaxed and have a new client software that is (apparently) easy to use. They are also the only other network with anything like the pilots or atc levels of vatsim.
Obviously there are times when the pilot and atc levels are higher than others, evenings and weekends for your particular country for instance.
The busiest places to fly on Vatsim are USA, UK and most of Europe. So you can fly sometimes with full atc cover from (say) Heathrow to Oslo or Milan etc.
There are always transatlantic flights going on.
If you want a sneek preview probably the best thing you can do is download and install servinfo, which shows all the pilots and atc online at any given moment. You can see the aircraft and click on them and see who they are and there flight plan etc.
Its available at
http://www.avsim.com/hangar/utils/servinfo/