This might just be a Tool fanboy answer (well, it definitely is) but it does sort of add to the whole air of mystery surrounding everything that Tool do, because their methods are so unorthodox and the waits for new material so long.
On another note, while Lateralus is probably my favourite Tool album/favourite album ever, on a purely song by song basis (excluding 'non-songs') Aenima is easily as good, if not maybe even better, in my opinion. Every single song on Aenima is near perfect, and it's maybe a bit more varied than Lateralus lyrically too.
Also, while I think 10,000 Days is a great collection of Tool songs, I don't think it's quite as great as being a Tool album. The appeal of Opiate through Lateralus to me is that they had this perfect flow and, more importantly, feel to them, that was unique to every release, that I don't quite think 10,000 Days managed to capture, at least for me. The track order also doesn't help, with the epic title track(s) being so close to the start of the album. So while I agree that 10,000 Days has some fantastic Tool songs (Vicarious, 10,000 Days, RIGHT IN TWO) Lateralus and Aenima, and even Undertow and Opiate just seem to have a more consistent and engaging flow, which is what I want from the new album.
[/Rant demonstrating Tool fans' pretentiousness]