Location. I don't care how pretty your venue is, if I can't get there easily, it doesn't make me feel inclined to try.
Travel to attendance ratio. I wouldn't mind an evening invite if it was down the road, but if I had to travel for hours, I wouldn't for anything less than an all-day invite.
The ability to leave when I want to. Partly linked to location. If I know I can leave at any time, I'm more likely to stay later. I just don't like the feeling of being trapped.
No waiting around. Or at least, no standing waiting around. If you must leave the guests milling around because you're sorting photos, can I at least sit down please? I only get grouchy if I have to stand in heels forever and ever.
Food and drink at sensible times. You're in control of the timings, please make sure I'm fed at appropriate intervals, or warn me to eat first. I get hangry. If it's a proper all-nighter, bring out snacks after midnight. I don't care if the food and drink is limited, but it would be nice if it didn't kill any of the guests, and if soft drinks other than water could be provided for those not drinking.
No beating around the bush. I'm happy to send you money, just don't be so blimmin' coy about it and stick BACS details on the invite. No cutesy poem either. Happy for a registry list too. Just, make it easy to find, please?
No shitty tables. You know who knows who - please stick people together who actually know and like each other! Invite groups of friends rather than one person from one random friendship group and another from your work. I'd rather be bumped off the list so someone else gets company they know, than to have to attend your wedding solo. Plus ones aren't necessary if you invite friends who know each other.
I don't care about your favours. It's your wedding, not mine, why do I want an oddly expensive tiny reminder? I will celebrate your big day with you, but it's between you and your new spouse to remember the anniversary.
Apart from the above grumblings... I'd ideally like to see that the wedding reflects both of you. I'd rather the food on offer isn't massively to my taste if it means you were bold enough to choose something you both like, rather than pandering to something to suit the masses. If I can see you made those personal touches rather than gave into pressure, it's quite satisfying as your mate. I mean... as much as I'm not a huge fan of weddings, if I've turned up, it's because I really do care about you, and I want to see you happy. Do things your way, not to suit distant relatives.