They almost definitely have less people on at the same time, so you may not get the "community" feel from a real server. Other than that, it depends on the host and whatever modifications were made (rates, etc)
EDIT: I actually played a private server for WoW in the first few days it was released. It was practically deserted but I guess they should have improved by now.
I do not play MMOs since Phantasy Star Ep1 on the dreamcast but for shoot 'em ups and games where private servers tend not to be encouraged if you can find a populated one then they are generally great.
The extra minor technical hurdle (sometimes artificially enforced) seems to weed out most of the morons that plague online gaming (OK sometimes to replace them with cheating morons but that is solved easily enough and at worst will have only cost you some time).
Spend a few minutes reading up on their forums/irc stuff/mailing list/wiki/usenet support (use something like http://groups.google.com/ if you lack usenet, I have not played with it myself but it works for some people I know).
I played on private servers for a bit and I must say it spoiled the game completly all the down time and lets not even mention the bugs! my pet raptor turned into a wolf and couldn't attack anymore because they added the 2.3 patch(insert 100 more bugs). Now you may think oh its only a pet but I spent many hours getting my pet skills and leveling him up and I couldn't do anything about it. I got fed up and decided just to pay for the game and im glad I did! World of warcraft is always something you can come back to and you grow attached to your characters so you want them to be safe and secure. If you want to waste your time and want your character to be fu**ed after each major patch comes out, sure go ahead play on private servers been there done that and I must say STAY far away from them. Also what happens once you reach level 70 and its time to get a group together to do 10 man raid then you think to yourself "lets get a group together" oh wait there is only 5 level 70s online at the moment damn I cant get the group I need. Also what happens when you get to outland and all these group quests show up? its hard enough getting someone to do a group quest with you on offcial servers nevermind on private ones. Well let me end this private servers=waste of time.
EDIT.. before you ask I tried about 20 servers including the most popular one! I'm not going to say any of thier names as that would be breaking one of the gbatemp rules.
Now let me tell you about questing there is alot of bugged quests on these servers and I mean alot of them! Now I would be doing a quest then half way through it find out it was bugged. So what do you do if that quest provided you with better gear than you already have? tough nothing you can do about it. Lets not even talk about battleground you wait long enough to play on offcial servers nevermind private ones! goodbye pvp if you play on a private server.
i've never played a wow private server... but yes i did play some others.
One thing is that you cannot just trust anybody that says they played a game private server.
The first thing is that for a private server to be there, you need to hack into the game and get the source code out, and you make a copy without some of the features. That means if you had the source code of wow, and you changed around with the paying part and everything then you would be able to play it.
Many games do not have a private server, and some are just ID/password scams. One game that is currently known for 90% of the players to play on a private server is ragnarok online from cloudphobeia (i think that is how you spell it)
You can't just make a private server in a blink- you would need the source.
Now how it feels about playing on a private server? it feels more like cheating rather than playing.
Private servers can always be modded so you can have a 10 times faster level up rate and you know- if the person that controls the private server chooses to edit something, then it becomes edited.
A wow private server is just accessed by changing the server it refers to in one of the log files (via notepad), and games like ragnarok, etc, don't have such easily accessible server names, causing the need for one to "patch" the exe file which just causes it to refer to their private server site rather then an official one (easier then it sounds, but if you do use a modified exe file, just be cautious of who you download it from, and check it's file size compared to the original). Most of the private servers out there attempt to be like normal servers, ie no leveling up instantly, so it doesn't make it seem like you are 'cheating'. Also, you don't just "get" the source code for something, making a program is usually a one way process and the only way to get the source code would be from a leak from, someone who actually codes the game (and seeing as their paycheck relies on the fact that no one else has the game they made, it is extremely rare)
EDIT: there isn't a single true statement in your post :|. Joined 5 days ago? Oh I get it now..
Phantasy Star Online Ep 2 dreamcast & pc- hackers item hackers evoryware
Ragnarok online - depends. some are quite popluated and run good WoE some of the privet servers will limit the atack Speed from the offical server making a super doped weapon pointless (on the offical server and some of the hack servers there is no limit imposed so you can get a literal Stream of atacks flooding the screen. its the most impresive thing i have seen in a while.
Gunz - privet servers make it easyer to get itmes that in the offical game are "pay to get"
World Of Warcraft- played on a server that had the level gap rased so much that you could solo raids... yah
a privet server is ok if you like it quiet. but you lose what makes a mmo a mmo
if you want to try out a mmo email the company (regardless who they are) and ask for a 15-30 day trial. they will gladly let you play in hopes that you get hooked and subscribe.
if you want the mmo feel without the "paying" do what i do hop betas
look up s4 league ^^ its in BETA for pc right now and coming out soon for the sony psp.