It is hard to predict which games will some day be considered rare. Now, while it is hard to speculate what will be in the future, let's look at the present and take the Atari 2600 for example, of which game cartridges were produced 30 years ago. Had you held on to them, would you be rich?
Well, most games are not worth that much (for example many games are not worth even $10 when they are new in the box!). For games that did rise in value, the condition is very important- if it's not new in box then the value lowers dramatically. If it's not complete in box, the value lowers even more. Though if you at the time, for example, made the choice to hoard many copies of a chasethechuckwagon game (which is considered pretty rare) and have it in new condition, you would be making a nice profit today. Again, at a certain time it is hard to predict what will become sought after vs what will end up at the garbage bins. Also, there are counter forces- as soon as you release your "hoarded" copies to the market, the perceived rarity of the item decreases and value decreases as well. A good example of it is Marvel Vs Capcom 2 for the PS2. Up to like a year ago, it was pretty rare to see those in the market and it was fetching up to $400 for a new copy, and perhaps $150 for just the game! But then, people caught on and flooded the market with it, trying to cash in, thus dramatically lowering its rarity and value.
Now, back to modern games. Is it worth to buy just for investment purposes? I think not. I see most of the modern games ending up in a future garbage bin. If you must, invest in some title from a well known series that would be remembered in the future. Maybe Final Fantasy. Also, another type of games which are worth investing in is those with limited production (Such as the Marvel Vs Capcom that got discontinued. Look for games that are suddenly discontinued from production prematurely. Although this doesn't guarantee the game will be worth anything in the future (and it most likely won't be), it raises the chance a bit. Also, if you do end up buying for investment purposes, the most important thing is to keep it in original, new condition. If you must play the game, get another copy for playing purposes.