So I just started using the site. So far it's the most promising of many sites/tools that I've looked at.

Unfortunately I'm still hitting a few brick walls and/or large mountains that are hampering my ability to make good use of the site - particularly in the area of organizing my library of >1000 PC games (I haven't even tried to tackle console games, which would require 100% manual entry):

1. I'd like to tag my games with genre and other attributes to help me with filtering and to remind myself about attributes of a game (e.g. which MIDI synthesizer to use when playing). Unfortunately I seem to be able to only add one tag at a time to one game at a time. For a library of my size, the tag feature is basically useless - which is frustrating because it has amazing potential for me.

2. I own multiple games on multiple sites, via various means (bundles that include keys for multiple sites, GOG Connect, accidental re-purchases, etc.). Unfortunately Completionator tracks multiple copies of games as separate entries, which adds to the work of managing my library and makes it harder to track completion (there's no reason to beat both the GOG and Steam versions of a game in 99% of cases, and if I wanted to track that I could do it by notes and/or reserving half of the completion percentage for each version). I should mention, however, that the current system would be more useful than ignoring retailer altogether, as it's useful to be able to tell which digital retailer's library a game is in.

3. I can't (un)backlog multiple items at once, and I'd like to be able to set up a queue of backlogged items to help organize my play time. As a gamer that has grown up and now has kids, time is my most precious resource, so anything to help me spend my gaming time more efficiently would be amazingly helpful.

4. Completionator doesn't seem to provide common data that would be useful for filtering, such as developer, publisher, original release date (or year at least - I'd love to be able to take release year into account when deciding which game to start next).

What it unfortunately comes down to is that the only immediate use that Completionator can serve for someone with my size of library is to help me avoid accidental duplicate purchases by letting me quickly determine whether I already own something on Steam and/or GOG. Any additional benefit is likely to come at the cost of a monumental amount of time spent on data entry/management.

Thank you for your feedback! I know managing a large collection is a daunting task and I'm hoping to continue to improve the site so everyone spends less time managing their collection and more time playing it! Here are some thoughts for each of your pieces of feedback:

1. You're currently able to add as many tags as you want to a game (not just one at a time) in a single edit, but as you stated, you must do this one game at a time. Being able to bulk edit items in your collection (and specifically tags) is one of the most commonly requested features and is definitely something I want to add. I've been trying to figure out the best way to handle it, so it's sort of stuck in limbo until I figure it out. I have some ideas though.
2. If you utilize the completions feature, you may have noticed the options for updating the progress status and backlogged flag when entering a new completion. If you leave them enabled, these will update ALL items in your collection for the selected game and platform. So if you beat The Witcher 3 on GOG, but also own it on Steam, when you enter a completion, you can have it update BOTH entries in your collection. Of course, this doesn't help you if you're just starting out and back-filling your statuses and such or if you choose to not utilize the completions feature. Again though, I think this is where bulk editing comes in.
3. If you haven't checked out the Playlist feature on the Profile page, you may want to do that as it can give you a flexible short-term filtered backlog of sorts. It currently has no ties to your collection (or anything else on the site), so you can manage it independent of everything else (for better or worse haha).
4. The site does have hooks for developer, publisher, release dates (including an "original" / "first" date), as well as things like play modes (single player, online multiplayer, co-op, local multiplayer), genres, franchises, and types (i.e. official release, unofficial release, mod, hack, add-on), but unfortunately, the data is manually curated and is a HUGE ongoing task. Until we can cover a little more ground with that data, I'm resisting the urge to provide them as filters more prominently (some of them are available on the Browse Games page) since it's so incomplete.