online
You will encounter alot of elitists concerning online play with this game. For the overwhelming majority of people playing any game, online is the online thing available. Not all of us live in major metropolitan areas or are college students with the time to go hang out around some vidja game store talking bout vidja games. Not all of use play in/care about tournaments. Dont worry about them, first of all.
Secondly, online with MK used to be pointless. The game's netcode was the worst I have seen in a long time, worse than trying to play CS on a 14.4 modem. But, its alot better now. Keep in mind, this game is peer to peer, and therefore your online experience is only ever going to be as good as the person with the shittiest connection. Do everything in your power not to be that shittiest connection. Turn off all your porn, all your netflix'n, all your VOIP, and make your grandma stop downloading meatloaf recipes while your playing. Even if things are perfect though, you will still sometimes have problems, especially if your ISP sucks or your hardware is not configured properly and of course if the other guy is the weak link. I have a blazing fast, business class fiber-optic connection and the majority of the time now (since the game has been patched and the network issues improved) i can get a game that is wonderfully playable and mostly lag free. However, UE3's networking framework was never stellar, and NRS is not exactly the most experienced developer when it comes to vast multiplayer projects like MK. This game does not handle latency very well, and its partly due to the fact that its a fighting game and even if both players are pinging each other at something like 30, its going to effect the ultra precise, pixel perfect timing based gameplay. If everyone in your game of halo, or whatever other silly manshoot your playing, had a ping of 30 you would be in hog heaven. In MK even when things are perfect there is going to be a noticeable input delay. It causes those precise timings and combos you have learned in practice mode to function differently. Sometimes you will go for a deep jump kick, and nothing will happen, because you pressed the button when your character was in the perfect spot, but the latency caused the kick not to activate until you had already landed. These things make ones brain itchy, and can be frustrating.
But you can compensate, and its not all that hard. If your getting a good connection, you can fairly easily teach yourself to compensate for a degree of lag. Some characters its harder, some its easier. You need to learn what combos are lag friendly and which arent. Anything with a dash in it will be exponentially harder, but not at all impossible. When you do something cool in practice mode, sometimes you have to look at it and say "Hmmm, how can I make this simpler and easier online, without ruining it?" Sometimes you gotta accept that you need to drop a few moves out of your combo, skip moves, do other moves instead even if it means less damage, just so you can get your completion chance higher online. Eventually, if you stick with the character and give it effort, you can do everything online you can do locally. The elitists are right about one thing though, and that is that online MK is somewhat different than local MK, enough so that it changes the experience.