Just a quick note...
Seems like there's a new and interesting development coming in the Bleach manga. We already know that Ichigo somehow, by learning the Final Getsuga Tenshou, ascended to a level higher than what a regular shinigami can. We also know that he wasn't the first one to reach that level, his father Isshin also reached that level of power in the past and suffered the same fate. They both lost their shinigami powers.
Now Ichigo has regained his powers, in a quite unremarkable way, but so did his father but for some reason, he didn't want to reveal that for a very long time (either that or he just postponed getting back his powers, since anyway it was a sure shot thanks to Urahara Kisuke's genius mind). Ichigo now has his shinigami powers back, thanks to a jolt of reiatsu from the captains of Seireitei and the revealed fact that he didn't actually lose all his shinigami powers, more like his shinigami powers machine run out of batteries (Rukia pretty much stated this as the fact that being a shinigami is an imprint of the soul that shapes reiatsu and transforms it into its weapons and strength). But when he lost his shinigami powers, Ichigo started developing as a regular human, just like his friends had, Inoue, Chado and Ishida did long before him. Since he focused and relied on his shinigami powers for so long, he initially wasn't aware of his human powers thus he wasn't able to see spirits anymore (nor were they strong enough for that, more in a minute). You might think "but how did he see Rukia at the beginning of the manga or the other spirits he gave flowers to?".
Well, that's because there isn't a strong boundary between the nature of these powers we see in Bleach. They all emerge from one soul, in different forms: one is human flesh (the congruence of good and evil in one safe container), one is shinigami form (no body to contain the soul but the soul is mostly controlled by good will and self control) and the other one is a hollow (no body again but this time the soul is mostly a slave to its instincts). When Ichigo used up a big part of his reiatsu to counteract the immense spiritual density of the Hougyoku in Aizen's body, he used the same reiatsu that was powering all three forms of its manifestation (human, shinigami and hollow). Yes, it's not that his hollow form had more reiatsu that it was stronger, it was because, being driven by instinct and exhilaration, it could harness a lot more of the soul's reiatsu (you might think of reiatsu as the density of the matter that makes the soul, or the pressure in that matter, because the shape of the soul doesn't always change and its shell can never be destroyed). So, basically, Ichigo got weakened and instead had to do training by physical and mental exercise to gather up reiatsu. He started recognizing reiatsu stored in objects around him, especially objects that he had with him all the time (his shinigami badge) and learned to harness it according to his spirit's "imprint" as I called it earlier.
Now he can see spirits again (and his dear Rukia of course), got a big jolt of reiatsu from the captains and got his shinigami shroud back but since his human form developed, his shinigami form looks different now, just like how his hollow form changed his hair, his height or his mask, while developing. There's a reason why his forms developed in the order they did: the shinigami form developed first because he desired to protect his family and friends, his hollow form developed next because of his despair in front of stronger enemies and his human form last because it's a safe container form, the one that's most hard to influence. Ichigo had to lose all his powers for this form to develop. Please note that it wasn't despair that helped this form develop this time, it was his will to protect his friends again (and to see his shinigami friends again). There was a brief moment of true despair where no evolution could have resulted from it and that was when Ginjo stole Ichigo's powers but thankfully Rukia and his other friends saved him.
Here's a good question though: why does he have to switch to his shinigami form before he switches to hollow form? I believe that only was before he achieved the Final Getsuga Tenshou, because he needed to do a normal ascension in "release states", but I don't think it's the case anymore (which is kind of sad if we don't see Shiro-san again?) since, when he fought to learn the Final Getsuga Tenshou, he fought Tensa Zangetsu mixed with his hollow form. I believe his nature now is a bit different: he looks like a shinigami + a bit of human-side intervention but he's got his hollow's control over power by trusting his instincts more and himself as well. He's not afraid of using a high risk, powerful strike from the start of a fight now because he's more confident he can control it. I believe there's still a level of uncontrollable hollow-like fighting prowess in him but the level of despair he needs to reach now to get to that level must be way higher than everything he has gone through so far.
I'll end my "quick note" here. Hope you read all it and liked it and maybe have something to say, in which case you're welcome.