Amazon on Tuesday sweetened the value of its annual Prime membership by offering 20 percent off pre-order and new video game releases. Naturally, there are some caveats you'll want to be aware of ahead of time.

The deal is valid for all physical video games (digital downloads aren't eligible) during pre-order through two weeks after launch and includes Collector's Editions (console bundles don't qualify). Only games shipped and sold by Amazon are eligible meaning titles sold by third-parties won't get the discount.

Amazon says the savings are automatically applied at checkout so you may not see it reflected on the product page. To determine if a game is eligible for the 20 percent discount, just look for the offer message on the product page.

Do note that the discount is only applied to games that aren't already discounted more than 20 percent. If a title is on sale for more than 20 percent off, Prime members will get the cheaper sale price instead of the discount. If a game is discounted less than 20 percent, subscribers will automatically get the 20 percent off discount instead (there's no stacking).

The move allows the e-commerce giant to better compete with companies like Best Buy and GameStop, both of which already offer membership programs for video game purchases. Amazon's Prime is a bit more comprehensive as it includes an array of perks that extend far beyond game discounts.