I was/am in the same boat. I bought the 2013 Nexus 7 within the first month of its release, and I've enjoyed it very much. The Nexus was an upgrade to an older Samsung Tab 2 7.0. At the time I was anxious about the lack of Micro SD slot, so I opted for the 32gb model. I've never felt a lack for storage.
I saw the Tab Pro in one of their recent TV commercials, and decided to check it out. I bought it very nearly on impulse, after doing a small amount of online research and handling one in person at the local big box store. All the online reviews nearly raved, citing only "average" battery life as one of the few drawbacks. Well, after owning it for two days now and comparing it to my 2013 Nexus 7, I'm trying hard to love the Tab Pro 8.4 but just not feeling it yet.
Yes, the screen is big and bright, and multi-window is pretty cool. I like the comfort of knowing I have a Micro SD slot and can stuff the 128 GB card in there some day. But that is where the joy ends. The screen is NOT better than the Nexus 7, only bigger. I can't notice the slight increase in pixel density (323 vs 359), but I quickly noticed the difference in contrast ratio and viewing angle. I guess it is a case of clever marketing, where they know bigger numbers (more pixels) sell screens. The Tab Pro screen is bright and works well for the desktop and applications, but simply is not as good as the Nexus 7 for watching movies. There is a distracting silvery shimmer to any letterboxes and the color is not consistent from one side of the frame to the other. One side has a slight silvery-bluish hue, while the other is greyish-brown. Extreme off angle viewing just results in a washed out low contrast grey hash. Even when you are on angle, the Tab Pro 8.4 does not pull the same level of detail out of the dark sections of images as the 2013 Nexus 7. Ignore the movies, and sometimes the text suffers too. Certain web pages have an odd softness (blurriness?) to the text, and again the contrast ratio just isn't the same. Black text on white background is not as precise as the screen on the Nexus 7.
Mind you, I am being extremely critical. But, for the nearly four hundred bucks I paid and the glowing reviews I had read, I expected better. I've also experienced the mystery crackling noises coming out of the speakers when the Tab should be otherwise silent. I agree that it seems to be somehow linked to processor usage. I expect a muted Tab to be silent, but unfortunately this one is not.
I'm also having difficultly adjusting to the Samsung skinned UI. After using bone-stock Android for the better part of nine months now, I have nearly forgotten Touchwiz. I do not prefer the Samsung version of the settings screen. I'm struggling to find the "hide" icon for the on-screen keyboard. Why can't I use the DashClock app any more? I absolutely detest the mechanical "home" button. Did I already mention the multi-window feature is pretty cool? I wouldn't mind keeping that.
Physically, I do admit to liking the larger screen and confess that was one of the major selling points. However, I'm finding that in practice I tend to spend time holding my tablet one handed. The seven inch format is no trouble at all. The 8.4 is manageable, but just enough additional weight that I'm starting to notice. I can't quite keep the same balance that I could on the Nexus 7. I do this thing where I hold the tablet in my left hand during landscape mode. I tuck the lower left corner in the palm of my hand, hold up the short edge with my thumb, and support the bottom edge with my pinky finger. My hands aren't quite big enough to hold the Tab Pro 8.4 for long periods of time in this position, and I find I need to bring my right hand in to support the other side. Again, this is OK for portrait mode but I use my tablet quite a lot for watching movies, and landscape just doesn't cut it. I'd rather watch a slightly smaller screen and hold it closer to my face than struggle to hold a larger one.
I'm certain the Snapdragon 800 is faster than the S4 Pro in the Nexus 7, but honestly I haven't noticed the difference. I have noticed that I've only had the Tab for two days, and I'm already down to 6 GB free after loading some of my "essential" apps. I'm worried that 16 GB will not be enough, even if I can l keep all my media on the Micro SD card. If the Tab Pro had been sold in a 32 GB version, I would have gladly paid the extra fifty bucks for it.
Anyway, I'm willing to give it another few days but if I don't have an epiphany I think this thing is going back. The biggest thing for me is the screen. It's almost the old adage - it doesn't have to work good, it only has to look good. And the Tab Pro 8.4 does look good, but the 2013 Nexus 7 looks better. Only smaller. Heck, even my wife's old iPad 2 feels like it has a better screen on it, at least with regards to contrast ratio and viewing angle.
I think what I really wanted was a Nexus 7 with this year's fastest processor and a Micro SD slot, but the Tab Pro 8.4 ain't it. Did anyone else feel the same way?