Where Vita is PSP's successor:
-Like PSP, it follows the proper method of improving gameplay by giving developers more processing power. More than any handheld before it.
-Like PSP, it has a huge, beautiful screen. Again, moreso than any handheld (gaming-dedicated system) before it.
-PSP was the first console to have an always-running OS (XBOX only had a kernel, DC had WinCE only when the devs decided to use it) that can be upgraded to add functionality to existing games. Vita has an even more robust OS with true multitasking support. And unlike Android/Palm/iOS, the game gets priority.
-PSP was the first system ever to be online from day 1, and the first handheld to use the same online infrastructure/profile as it's console counterpart. Vita continues this and improves upon it. An improved web browser and Remote Play functionality. Your PSN profile is now integrated completely into the system where before it was an afterthought. There's even a model with a semi-permanent (3g) connection.
-PSP emphasized console-like controls with nearly the same amount of buttons and an analog nub. Vita goes one step forward with two proper analog sticks. It still lacks L2/L3/R2/R3, but it's much closer to the dual shock standard than any handheld before it.
-PSP launched with the single best gaming library ever. In one day it had caught up to the months head start DS had. I own about 10 times as many PSP games as I do DS games (and most of the DS games were bought for a controller). Vita looks like it'll do the same.
-It's still region free!

Where it's not:
-The XMB was one of the reasons I loved PSP so much. I loved that UI since it debuted on the PSX, that I was unable to get. XMB is currently the singular best GUI on any gaming system. The PS3 variant in particular runs circles around Wii/360/iOS/Android/3DS/DSi in terms of organization and intuitiveness. Sony abandoned it for something will slightly less organization than 3DS's.
-One of PSP's more useful features was it's ability to act as a USB harddrive. That meant you didn't need platform-specific software to manage your content. It also meant developers like myself could make programs that convert multiple types of media PSP didn't support into formats it did. Removed, in the name of security (through obscurity?). Vita even works in reverse now, instead of a USB slave, it acts as the master. Your PC doesn't dictate what files you move over, with it's superior interface, screen size and controls, the Vita does.
-With each model of PSP after the first one, PSP received upgraded TV-out capabilities. The 2000 got component-out, the 3000 got the ability to play games in composite-out, the Go got the ability to use PS3 controllers via bluetooth. Removed, due to the touch/motion crap which would be harder and/or impossible to use. And people wonder why I hate gimmicks. It detracts from other functionality. I fully expected next-gen TV-out capabilities. HDMI, and dual-screen support to do things you see ipads doing. My number 1 fear with Vita is a new model a year later with proper TV-out. I don't have that fear with the 3DS. Sure a remodel with a second analog nub is probably coming, but I don't need to buy it to get that nub on my 3DS. The $20 add-on will do.
-PSP used standards. Memory Stick and a proper USB port. Granted the Go didn't have a proper USB port, but it at least had an excuse (cut down on the number of ports to reduce size) Vita uses another dock connector, but it doesn't do anything USB didn't do already. It's literally pointless, it's less than pointless since it makes the unit less portable (now you MUST have that single-system cable with you to charge it) Even the semi-standard memory stick was replaced with a Vita-specific card that costs more. In the name of security and minimum speed requirements, which is complete BS. Windows Mobile 7 phones use microSD cards, it has strict minimum speed requirements AND it locks the card so only it can use it. MicroSD could have been used.
-PSP was a huge step forward for portable gaming. It was quite literally, current-gen console-quality. And one of the main reasons for that was UMD. It was extremely cheap to manufacture (less than $2 for 1.8 GB when it launched. To compare, DS cards cost $20 for 64 MB. Over 288 times more expensive per megabyte) to the point where flash STILL hasn't caught up in price 7 years later. Hell, a bluray disc costs less to make than 2 GB of flash. Had Sony gone with that, devs would have more space to work with, and we'd have proper backwards compatibility instead of Sony treating UMD like a vestigial organ. PSP 2000 and Go already proved UMD didn't use much power.
-UMD was an exponential step forward, we went from 32 MB GBA games to 1843 MB overnight. If you were to total up the amount of 128 MB and 256 MB DS games, there'd still be less than there are 3.6 GB multi-disc UMD PSP games. So how much more space do devs have on Vita than they did on PSP? 410 MB. An improvement by a factor of 1.1. That's not an exponential improvement, that's incremental. To compare, Vita devs have no more space than 3DS devs do, and they're already complaining about the cost of cards and lack of space. Vita games require more space due to the improvement in graphics/audio.
-The point of PSP was more processing power+space = better games. No reliance on any gimmicks. Just giving developers a bigger fish bowl to grow in, a bigger easel to paint on. While Vita improved on processing power in a big way, it brings with it gimmicks, gimmicks that cost it functionality in other areas. The rear touchpad is a big reason why there's no room for UMD, and why there is no removable battery. Both touchscreens and SIXAXIS/motion sensing are why there is no TV out or PS3 controller support. Then there are the 2 cameras. Both 0.3 MP, where PSP had 1 camera that could face both directions, and was 1.3 MP.
-And again, memory stick. Since Sony went backwards with cards, it makes sense they'd go backwards with saved data too. Now you don't have all your saved data in one place. Some games will save directly onto themselves, which brings back the filesize/quantity limitation (PSP games were all limited to 100 saves). And the games that do save on themselves, can't (at least for now) access the memory card. Meaning no DLC or updates.
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