The Invisible Hand is General Grevious' flagship - it appears at the start of Revenge of the Sith, fighting the Republic in the battle over Coruscant.
It's a big ship - as long as a Star Destroyer, though not as wide. Like all Armada ships it's prepainted, and they're done a good job, looking very good in the Separatist colours of blue and grey. The model detail is excellent and it should look great on the battlefield, even if it's not as instantly recognisable as ships from the 'classic' era.
As usual the Invisible Hand comes with a selection of upgrade cards. In particular it comes with not one but two admirals: Admiral Trench and General Grevious himself.
Trench has a similar effect to Thrawn, by allowing you to add extra command dials for your ships, though in this case each ship needs to have a matching command token first. He's a generically useful admiral who should work with any fleet.
Grevious' effect is very different, allowing you to refresh your defence tokens when friendly ships or squadrons are killed. This has the potential to make your fleet a lot tougher, especially given the fact that the Separatist ships released so far don't have any duplicate defence tokens. You probably want to run him with at least some squadrons, but he's got a lot of potential!
Overall this is looking like a good expansion with a lot of battlefield utility, and one that adds a lot of capabilities to the Separatist fleet - it feels like you've got a full range of options now, rather then the limited capability offered by the initial fleet box. The one downside is the price - the latest releases have seen a significant price jump, which will make collecting a full fleet a lot more painful for your wallet.