This game pwns!!!
The storyline is also impressive too, it takes place a year after the death of Sarah Fisher (the main character's daughter) and he gets busted by the po-po and brought in for questioning. So like 7 out of 9 missions are mainly flashback missions (don't worry they're all not from the previous Splinter Cell games) and they all work pretty darn well.
As for a sandbox approach wise? the sandbox approach is more on the Pandora Tomorrow side than Chaos Theory's, but hey that's not a bad thing at all! because there's probably alot more ways to complete my objectives than I thought in PT. But yes it has a sandbox approach and makes it very replayable.
All in all it's a great game. Yes it has flaws but what game doesn't? so if you're patient to learn the controls (which you'll pretty much pick up easily in like a few minutes or so) and looking for a good stealth game for your PSP, then this is for you