Now that Ace is becoming the largest recognised grading company in the UK, adding Ace grading along side psa and cgc for the grading company valuations on the prices. Would hugely help the UK users 

Actually showing a % of what I own compared to how many games were made for that console. Per Example: 388 Games were Made in the US and I own 85 of them it will then show 21% of the whole collection I own, also for it to tell me what I still need to complete the set.

I would like to be able to see the price of a game in my wishlist. Like this I can check at only this page when I'm in a convention to see if the price is good.

Let me 'watch' a listing so I can keep track of it when I come back to the site.

It would be great to see an average "review" scores on games on your website, such as Amazon or Metacritic provide. You might be able to screen-scrape review ratings from those sources. I would love to see both pricing info & basic overall review scores! That way, I'd know to keep a 4.5 star game worth $2, but ditch a 1 star game that's worth $100 for some odd reason. I often buy games in bulk, and it's difficult to decide to keep games or sell them. I often don't care much about "collectibility"...I only want good, fun games in my collection. I'll sell the bad ones that are worth money.

Allow users to input the date they purchased a specific game when they add it to their collection.

Your guide is good but needs improvements . There is no price-charting for japan games , japan consoles , commodore , amiga , trs 80 color computer , There is even more . Why do a job only half way ?

In the hypothetical situation where a single buyer wants to purchase 20 games I don't want to technically be charging $40+ for shipping when in reality I could probably ship them all in a large Priority box for under $17.90.