Any gamer around the age of 25, hardcore or casual, likely grew up on two consoles - the 8-bit Nintendo Entertainment System (affectionately known as NES), and Sega's 16-bit powerhouse Genesis. Nintendo introduced the world to the likes of the Super Mario Bros., as well as the brilliant and customizable racer Excitebike and the iconic gold cartridge of the incredible Legend of Zelda. Meanwhile, Genesis brought pure speed to the platforming realm with a blue hedgehog named Sonic, offered a slew of now-classic sports games, then tried to milk the success with the first console add-ons, 32X and Mega-CD.

The digital realms of Xbox Live Arcade, Wii's Virtual Console, the PlayStation Network and iPhone have helped create a retro niche in gaming, bringing back many of the big titles from before the days of CD-ROM, sometimes with updated graphics or gameplay. But these realms are limited to what publishers decide to republish on the new platforms, and many gamers are still likely sitting with a closet, drawer or bin filled with the old plastic cartridges, but no systems on which to play them. And it would be senseless to spend money on the same games a second time, but despite old consoles holding up surprisingly well (especially considering the failure rate of modern consoles), there aren't many Nintendo Entertainment Systems and Sega Genesis left in working order, and the companies no longer make them.

Enter everyone's favorite online nerd store, ThinkGeek, and a product dubbed the GenX Genesis/NES Game System. For $39.99, gamers can dust off the old cartridges from the competing companies, and relive the days when Nintendo only needed two buttons and a directional pad, not motion controls, while Sega upped it to three buttons, back when they were still in the console business.

This isn't the first time a company - ThinkGeek being one of them - has resurrected 8- and 16-bit gaming, with numerous clone consoles and even handheld varieties that use the original cartridges. For a long time, some were made on the margins of legality, but they have become more and more prominent as patents expire and less legal battles are involved in marketing such a product.

The novelty of GenX, however, in addition to playing the games once again, is that Mario and Sonic used to be the most bitter of rivals. Sega commercials famously used to say, "Sega does what Nintendon't." Between the Entertainment System, Genesis and Super Nintendo, the two Japanese companies found themselves battling through the early 1990s. Now, one cheap console lets gamers put Mario and Sonic side-by-side, and switch between them at will on the same console, with the same controllers.

GenX is smaller than even the slim version of Genesis, and comes with a power cord, a composite audio/video cable and two controllers. The console is top loading, like Genesis, which makes knowing whether the game is connected properly easier than it used to be with the American version of NES, which loaded via a side door slot and then had to be pushed down. The console simply has a switch reading 16-bit, off and 8-bit, and players give power to whichever side they're playing. There is also a reset button.

The controllers are Sega more than Nintendo, being modeled as a slimmer, slightly smaller version of the 6-button model created later in the cycle of Genesis. The big buttons - A, B and C - are in an arc on the bottom right of the controller, while the smaller ones - X, Y and Z - rest atop them. It features a standard D-pad.

The game system feels cheap coming out of the box. Part of that is due to how light the system feels in comparison to the originals, but that simply has to due with the technology getting smaller, therefore requiring less packed into the plastic box. But the power/selector switch also feels a bit flimsy, and the cartridges feel stiff going in and even more so coming out, especially on the Genesis side. That said, I've taken good care of my games over the years, and everything I put into the system - about six games on the 8-bit side and six more on 16-bit - worked without a problem. Even the Game Genie for NES (yeah, I used to be a cheater) worked without a hitch. This is obviously dependent on the condition of one's cartridges, which are notorious for collecting dust, but that's why we were always blowing into them, right?

The controllers included work much better on the Genesis side than NES due to the button layout, but aren't bad for games on either system. GenX even adds some functionality on the Nintendo side, making the C button a combination of A and B, and the Z button a turbo. It's a nice touch, but it would be better yet if players could customize the layout.

The console is designed with NTSC coding for the US market, but claims to also play "most" Japanese import games (I had none lying around to test this claim). At the end of the day, the choice of consoles will be up to the player's retro collection, or what they're willing to invest on eBay. For me, it's perfect, as NES and Genesis were my two consoles growing up. Others may want to look into ThinkGeek's Retro Duo NES/SNES Game System, which keeps things on the Nintendo side, or the Retro Mini X Handheld System for Nintendo games on the go. But with most digital retro games running between $5 and $8, gamers might find it prudent to get some more mileage out a hefty old collection for the one-time price of a GenX.