You're actually expected to go through the routine of thinking about the cases instead of using a walkthrough, thus only 5 mind-boggling cases. They're all long enough anyway o_o. I so wish one could skip the Investigation part.. I so hate it, court is more awesome ^_^
While that may be the intent, the player is frequently required to make leaps in judgment that most normal players wouldn't normally be able to figure out on their own--especially in court, where even just a couple of mistakes would cost you the case (I'm thinking of the final cross-examinations of Moe the Clown in JFA and Luke Atmey in T&T in particular). This wouldn't be much of a problem, except that making a continue point (at least in the first three games; I haven't played AJ) forces you back to the title screen, and you can't make one during cross-examination or when you're being made to present evidence. There's a reason the series shows up on TVTropes's Try Everything page; while figuring out the mystery on your own is fun, the fun factor is...greatly diminished, in my opinion, when the player is required to essentially guess more frequently than the character they're controlling.
Yeah, I used walkthroughs. I didn't mind; the stories and characters were still highly engaging. (Then there's the fact that I'd already managed to spoil myself as to the outcomes of the biggest cases...)
That said, I enjoyed the investigation segments, especially JFA and T&T's Magatama segments, for that very reason; I was able to work out bits of the mystery without the danger of a game over from a reckless error, and I only really consulted a walkthrough when I was too impatient to go looking through every area for some tiny piece of evidence that I missed somewhere and stuff like that. Not to mention how many of the various gags--I particularly liked the references to
300 and
Ghost in the Shell--were found during these segments.
I know characters grow but I don't like the new Ema. Klavier doesn't do what Edgey and Von Karma did for me. 
