Really, OK do best in larger games, though they can do well in smaller.
OKs also really do have a weakness. There is only one true 'ranked' unit, and this unit can do very little offensively. While the price is right, Gnoblars are really only suited to grabbing table quarters. They are much slower than the rest of the army, and cannot do enough damage to an enemy unit to keep the enemy from overcoming their static combat resolution score.
If you like the MSU strategy, the OKs are a great army. Several units of 3 or 4 Bulls, Ironguts, Yhettees and Leadbelchers can work over more traditional armies with relative ease. The unique shooting units of the OKs (Gnoblars, Trappers, Leadbelchers, Maneaters, Hunters) make for a nice change, and can really surprise an opponent. The Character choices are also very cool, though some (like the Hunter) will take a more experienced general to use effectively.
The army is designed to attack, and attack HARD, and it does not do so well on defense. It can be a good starter army, but I wouldn't recommend it off hand simply because it is such a uniquely themed army. There are simply too many important areas of the game that OKs don't touch upon, such as Fast Cav, Flyers, War Machines, and Chariots ( I know, I know, the scrap launcher fits both of these last two categories, but not with any real substance). Another, less specialized, army may suit a beginner better.