First, you can't hold the cards. I'm okay with that though, I'll collect items in WOW or other online games even if you can't hold them.

Second, the interface is extremely cumbersome. Yes I know that over time you start to figure out what things like, "yield to this card in the future" mean, (I still don't!). While this impacts gameplay more I still don't feel I get that convenience of sitting down and just flipping through my cards like I would with a trade binder. Perhaps more ways to customize the organization of your binder would placate me. Personally my binder is sorted by Colour -> Set (newest first) -> rarity (yes I keep uncommons in a binder) -> Alphabetically (with empty slots for cards I'm missing). How does this come back to Promos? In my cardboard binder, the promos become a centerpiece of each section, they stand out and people go, "WOW a foil skittles!". Online the interface is designed such that instead of being a showpiece it just gets in the way and 'foils' your organizational structure.

Third, and by far the most important, the graphics SUCK! If I own a $50 card that includes a piece of art, I want to enjoy the visuals in all their splendor. I have a hard time cherishing a card with unique art or foily texture when it's represented as a flashing, pixelated blob.

With modern high powered computers and broadband connections, there should definitely be an option for "display high resolution images". This may exist somewhere, but I've spent tons of time digging and I haven't seen it.

I'll admit, I am an MTGO noob. I really only use it for drafting practice. That doesn't mean I'm new to it though. I started my account when MTGO was first launched years and years ago. I was so upset with the implementation I immediately removed it. I checked back a few years later and it was still garbage. Last year I jumped on and found it "tolerable" but still far from what it could be. IMO what they've done is focused on trying to replicate the offline experience online, instead of simply creating a great online experience.

I've gone way off topic, so
/endrant