If one is a hold em player, after playing Omaha as a serious student for a time you will notice that with starting hands you will be playing less hands than in Holdem, and if you are playing 8 or better you will be playing even less hands then in Omaha high.
Omaha is a drawing game. It is rare for pocket pairs to win straight out at showdown. Big pairs really do not have enough value to make a hand all by them selves. Indeed any two holdem cards that may rank well on a starting range table, do not have enough value by themselves to give positive expectation to an Omaha hand.*
*Comments about expectation are general, things like if your playing limit or PLO, or the nature of your opponents that would effect EV are not within the scope of the question. I am using the term EV (Expected Value) loosely, as a ratio of value between hands, rather then the more standard way that assigns a actual money value to a hand.
The EV of all Omaha hands falls within a much narrower range then the EV of all holdem hands. The EV of the worst starting hand in holdem is more negative than the worst starting hand in Omaha and the EV of the best starting hand in Holdem is more positive then the EV of the best starting hand in Omaha.
On the flop the lose of EV is more pronounced then it is in holdem. In holdem you don't often hit or miss a flop with some hands like big pairs, or you may hit a flop with middle pairs and back door outs. Missing a flop in Omaha you are virtually drawing dead. Hitting weak you are generally drawing much thinner then you would be with Holdem. In other words what ever cards you have in your hand need to have a stronger piece of the flop in Omaha then in Holdem.
Whatever that piece of the flop is, the real quality of an Omaha hand unlike most holdem hands, is determined by what that hand can become, and what those cards in your hand defend against other players cards becoming.
To give you a simple example: your hand is 9945. Flopping a set of nines with the flop 789, is not really that good of a hand. Your straight draw is worthless, it is a gut shot and your drawing to the bottom end. If their are any suites on the flop, more players have cards to beat you. If the game is eight or better your value is even less.
Lets consider why you might play this hand as a holdem player. You have two reasonable holdem hands, pocket nines and 4-5. Pocket nines you would play from any position, and also have lots of scenarios were you might raise or call a raise. 4-5 a reasonable hand to play in late position when there is no raise, even more reasonable if it is suited. If your 4-5 suites hit either of the nines or bravo double suites with the nines, that is even better, and you just had your first "thinking like an Omaha Player moment", congrats.
If a holdem player is aware of outs they may consider playing either of these two hands in a mathematical context, that may go something like I have this many cards to make two pair, this many to make a straight, so many to make a flush, add those all up, and say to themselves that I have 18% chance of winning this pot, add a little EV for position and maybe even a little more EV because calling station Joe has called. In Omaha the holdem player might go through this and speculate that one hand has EV of 18% and the other hand has EV of 22% so they will give the EV of the Omaha hand 20%, and be the fifth limper in.
The problem here as any Omaha player will tell you is that there is no way this hand has an EV of 20%, this hand is junk.(Not to say it might not have an ev of 20%, the real EV is not known because you don't know what everyone else is playing).
You cant really think in those kind of holdem calculations. In holdem the complexity of the hand as a benchmark is (2x2), in Omaha the complexity benchmark is (2x2x2x2). When you look at how the Holdem player came to his conclusion, the bench mark formula was (2x2+2x2/2). One is not accounting for the complexity of the hands and can never come to a correct assessment of the hands EV.
If you consider this benchmark relative to the holdem benchmark, in a practical sense it presents some problems. Hand rankings and ranges are especially problematic. It is not practical to memorize the hands in rankings or to memorize the hands in ranges. It also makes counting outs simply impractical as a consideration and outs are not really all that valid like in holdem, post flop in Omaha.
Typing hands in Omaha is the basic nuts and bolts of figuring out the ranking of an Omaha hand on the fly. We know the ranking of Holdem hands through card sense or memorizing of ranking tables, but in Omaha you need to understand what makes a hand rank, because it is not simply about the value of the cards, it is also the value of the how the cards relate to each other, and how they relate to your opponents hand. In Omaha saying your cards must work with each other is a severe understatement and saying your hands should consist of high ranking cards is also a severe understatement.
A really great hand in Omaha high, much less great in eight or better is A-A-K-K. In holdem, any AA,KK,AK hand has a very high likelihood of success. These are all rank one hands in every holdem ranking table. Hard to play them bad, even harder for any player to think they may have played them badly when they won with them. All you really do when you play these hands is think about maximizing the pot size until you have reason to believe that may not be wise.
In Omaha like all Omaha hands, this hand is simply not that great until the flop. All Omaha hands sit within a very narrow range of value compared to all holdem hands. Typing any hand before the flop is relatively simple and mistakes do not have near the impact as misjudging your hands value in holdem.
There is lots of information about Omaha starting hands in books and online. Bob Caiffone wrote the Omaha bible and that is were you should start. Starting hands are generally good if they start as wrap arounds or pairs with kickers that wrap near the pairs. Suits marginally improve the hand, if your a strong player. Large suits improve the hand. A hand like 8,9,10,J has more outs then a hand like AAKK. Two pair or OK, much better if the pairs connect to each other, a little better if they are suited. But the real conversation about what makes a starting is about what makes that hand work (or fail) on the flop.
In Omaha the flop is were your hand becomes! That subject is complex and deep. Way beyond the scope of the question. But this complexity is directly related to ones starting hand, making that a large part of the discussion. In a very basic way many starting hands are a lot more trouble after the flop in Omaha then they are in Texas Holdem. Counting your outs after the flop in holdem is a reasonably accurate way to assess the value of your hand, in Omaha it is only a small part of assessing the value of your hand. You determine the value of an Omaha hand according to its type rather than according to its rank.
I would like to say to the OP that I hope you have a little better understanding of starting hands in Omaha compared to starting hands in Holdem, but I am the OP and that would be strange.