What were you unimpressed with?
I do love the design, the keyboard does look cool, but the from reading the reviews, people are split on the keyboard, some didn't like the larger keys, others not enjoying the decreased key travel, others were not bothered at all buy it. Without using it, I think I like the design of the keyboard.
I do think apple went to far in the name of thinness, but it is a beautiful machine. I don't think going from a 2011 MBA to a 2015 rMB, you'd notice any performance increase if the benchmarks being reported are accurate (and there's no reason to disbelieve them).
Quite a bit of performance increases, but more importantly lots more battery life.
Geekbench scores are about 12-15% better at minimum, and at best we're seeing geekbench score differences (e.g. at everymac) in the 20-30% range. That's quite significant I think, we're talking about differences the size of MBA vs rMBP.
GPU is also a lot better. The new MBA can run twice as many high-res displays, and even do 4K res at 60 hertz.
It's SSD is MUCH faster. Even compared to 2014, the 2015 SSD is 2x as fast. The 2011 is on an old SATA connection, the 2015 on PCIe x4 that you don't often even see in desktops.
Faster wifi, usb etc.
And lastly, battery went from 7h to 12h. And if you've had your MBA 2011 for 4 years, it's likely you're going to go from less than 4h to 12h.
So I'd definitely be happy with the upgrade.
As for the rMB... I'll have to use it first. I'm not huge on the retina displays. I tend to hook into an external display at home (so retina or not, I'm not using it). And on the move, I tend to do word processing, email, blogging, I really don't need a retina screen for that. It's a nice bonus, not a necessity.
The dongle requirements are a joke (I'm writing this with a charger, two USB and HDMI plugged in to my rMBP). The price is quite steep (rMBP level, upgraded MBA level. Its performance in comparison is a joke). I think I can get used to the travel on the keyboard, but it's definitely a bit of a step down for thinness I didn't really need. I don't carry computers in my hand while walking down the street, not even my iPad, it feels weird and can get snatched. (city life). So with this thing in my bag or on the table, once you get into MBA-range weight/size, or even rMBP, I don't really care for ultra thinness. Again, it's not in my jeans or in my hand like a phone, it doesn't to be 1 millimetre thick.
So yeah not excited about it. I'm glad it's here because in 2 years or so, it'll be an excellent buy, when my charger is a dongle, I get a 2nd USB-C port, a high-res camera, a 14" version (the size of the 13" MBP, but thin), with an extra 2h battery life and a bit better performance. Yeah sign me up. But not today. A bit like how the MBA started as an $1800 expensive, low-performance device in a world that wasn't fully wireless / cdless yet with 5h battery, and became a sub $1000 consumer powerhouse with 12h battery over time.