Unsolicited plug here, but ogre kingdoms are cheap cheap cheap to start, require much less models for assembly/painting, are very competitive in 8th (maybe not top tier, but
very solid) and have one of the best battalion deals of any
WHFB army (the absolute best from a pure $$$-savings standpoint, and it's all useful! you just have to convert the leadbelchers, which is easy with all the extra arms you get on bull and irongut sprues).
Monstrous infantry are Fun in 8th edition, as you get full attacks from the second rank. You can also throw your weight around and not get rolled over by enemy blocks as easily as an army like high elves will (unless you build/play them well, of course).
Buying ogres to use as chaos ogres for my
WoC, I'm continually amazed by what a good deal their boxes are. 6 bulls for $40, or 4 Ironguts for the same price. Whereas for river trolls (which are admittedly a newer and very excellent sculpt) I pay $45 for 3! With much less extra bits to go around. You also get tons of gnoblars on the ogre sprues that you can use as their own unit!
So that ends my plug, but
imho they're one of the most under-represented awesome armies in 8th edition, I can't figure out why more people haven't started them. Whereas by contrast, everywhere I've gone has been saturated with
WoC players (out of 11 Dakkanauts playing at DakkaCon, 4 of us had them).
WoC is awesome, but extremely common, and even moreso now that 8th edition allows some very powerful builds for them. Whereas Ogres got worlds better in 8th, but everyone had abandoned them in 7th and seemingly they are still a rare sight, at least at the stores / small tournies I've been to.
Well, it was worth a shot

. Obviously they captivate my interest, so I believe what Mannahnin said is most important- you've got to really like the models/feel of an army to stick with it, otherwise you'll abandon it before really learning how to play it well or finishing painting it.