The most important street in omaha (assuming sufficiently deep stacked 100bb+) is the river. The majority of your profit or loss will come from the decisions you make on the river.
You need to know when and how to value bet, when to run a bluff. You can't only value bet when you have the nuts - you have to make thin value bets sometimes. You have to know how much to bet. Maybe you make a big bet with the nuts hoping they will think it is a bluff, maybe you make a smaller bet hoping they will call you lighter.
You can bluff the river sometimes but you have put a read on your opponents and read the board texture to find good bluffing spots. You need to figure out which of your opponents will bluff the river and play accordingly. Some opponents bluff at inopportune times - they miss their draws and figure "I can't win by checking" so they bluff, and you can call them on the river with as little as one pair. Some will never bet the river without the nuts or the near nuts.
I often see players lose value by not raising the river with 2nd or 3rd best full house. Depending on the board texture and the action, sometimes it is correct to just call, but often a raise is correct. Sometimes players make mistakes by raising small full houses in situations where they are never getting called by worse hands. In one hand today I had JT99 and double-barrell bluffed a 556Q board. The river was a 9 and my opponent raised my bet with 569x (he had a 9 in his hand too, so this was a pretty sick one-outer). This raise makes no sense - if I'm bluffing I will just fold, but if I have him beat he's costing himself almost a full buy-in for the game (we were something like 200 big blinds deep starting the hand).
Preflop and flop play is important too, but it comes down to math, you are looking to flip coins getting slightly better than even money odds. But it takes a lot of 60:40 coinflips to make up for the EV of one bad river call for 50bb. And picking off a river bluff for 50bb can make up for a lot of questionable flop play.
I really feel that river play is the most important skill in pot limit omaha. Hope you enjoyed my rant.
