The Cap stuff is very, very enjoyable. Starts a little rough, but otherwise It's top shelf silver age Marvel.
I got the first Omni as a gift along with a couple other things. I fucking loved it. The second omni is pure 70's Kirby insanity. Madbomb and Kirby Falcon alone make it worth the price, imo.
Madbomb is one of those comics that I have to stop myself from reading again every time I think of it.
If you like Kirby, you owe it to yourself to at least read the CA stuff on unlimitef.
Also, a word of warning. I love Kirby Thor, more by far even than Simonson's, but the inking is mostly Coletta and sometimes it is painfully bad.
Also start with the second Omni, the series really finds its way at about 121.