It's a good day to be an NVIDIA SHIELD owner. Valve's Android ports of PC shooter classics Portal and Half-Life 2 just dropped in the Play Store for $10 a pop. They're only for the SHIELD (even other devices with the Tegra 4 chipset aren't invited to the party), which is a bit of a mixed blessing - these games really require a full controller to play.
Valve teased an Android release for the 2007 classic Portal way back in March, but we only heard about the Half-Life 2 port last week (via crowbar). Since both of these games run on an older version of Valve's Source engine, it makes sense that it didn't take long to get HL2 up and running once Portal was finished. Ryan Whitwam got his hands on an advance copy of Portal for a full review if you're on the fence about a purchase. Half-Life 2 should be essentially the same, at least in terms of performance.
If you're the kind of gamer who likes a solid, rounded experience, and especially if you're a fan of physics puzzles, go for Portal. It's a fan favorite for a reason: the dimension-warping gameplay is a pillar of modern gaming, relying more on careful thought and planning than pew-pew shooter skills. The short but sweet story is also a hoot, thanks to Ellen McLain's timeless performance as the sarcastically murderous AI GlaDOS. If you'd rather go for a more straight-laced shooter with a longer story, Half-Life 2 is your game. Its action-packed and lengthy single-player campaign has solid gameplay and science fiction story elements, not to mention some great characters and unique weapons. Make room: both games weigh in at over 2 gigabytes.
And if you're just a fan of Valve's games in general, you stopped reading about two paragraphs ago and your wallet is already $20 lighter. It's worth noting that the NVIDIA SHIELD is on sale for just $199 at the moment.