I've had the RT5 for about a week now and honestly, although it could have been better, I'm not disappointed by it either.
For reference, I have a pair of KEF Q500, Q100, Q200 center, SVS SB-2000 sub hooked up to a Yamaha RX840 in my living room. They're not high-end I know, but I think everyone agrees that they're pretty good mid-end stuff.
Now the Sony RT5, why did I get it? For my small-ish game/bedroom (about 8x12 ft.). I don't really have the luxury to get bigger speakers in there and since I was offered a pretty good deal on the RT5, I thought why not? Let's try it.
To cut right to the chase, which is the sub. I agree with an earlier post, it is one-note-ish. But is it really that bad? No, not really. I mean, if you've heard the older down-firing subs that Sony was so fond of on the CT770, CT660, and CT260, NOW that back then was some terrible sub. It was full of bloat, no balance, bleeds into the mids no matter how you adjust it or place it. The sub on the RT5 is actually much better than its predecessor, sure it is still mediocre but it is no way I'd say "bad".
As for seperation of the channels. Show me a soundbar which has better sound seperation than the RT5 at the same price point. You won't find one, I guarantee it. Yup, the bar could have been longer and the drivers bigger. But are most people willing to pay more? Nope. Design and economics goes hand in hand, there's no 2 ways around this as long as money drives everything.
With that, I think the sound seperation on the RT5 is decent enough. I don't have issues pinpointing players in Destiny on a Crucible/PVP match. Nor did I have much of an issue hearing where footsteps are in direction when playing stealth heavy games like MGSV. Sure, it's not ever going to be as engaging as my KEF setup, but I know the limitations of a soundbar + 2 rear channels design, of which didn't dissapoint me. If anything, I think Sony surprised me that they are still able to have a good soundstage with pretty good (in my book, since I do game semi-competitively) audio cues. The rear speakers may sound narrow in its soundfield, but for my bedroom I think it is adequate.
As for the treble, yes it could be more energetic, more sparklish with some aggressiveness. I wouldn't disagree on that. I think Sony could have done better with the tweeters than just bring it over from the CT770/780. If anything, the treble on the RT5 is rolled off, too smooth in nature. But thankfully at least to me, it didn't make the high-mids or highs sound dull or muddy, there's still a good bit of air in those areas. Be glad Sony even had tweeters in this system in the first place, because they could have easily snuck it out.
So my whole post may sound like I'm defending the RT5 or it's some paid opinion piece or something. Well, I AM defending the RT5. I think for its price, it has damn well shown its worth. There aren't many soundbars at this price that provides 4k60p passthrough, may not even sound like a big deal to you if you don't have a PC to game on at this resolution, but once or if you do, it's a Godsend. 4k, 60fps is an absolute bliss. Couple the other fact that the RT5 has very, very low input lag which is another great bonus. Something that every other soundbar out there couldn't compete against with.
The Sonos Playbar, Play1 rear speakers + Sub does sound better, I'm not even going to argue on that point. But LOOK at the price you'd be paying for to get all that. You might as well go for a mid-end system from KEF, Wharfedale, Q Accoustics, etc. etc. + a midrange AVR to blow the socks off the Sonos combination, for probably the same price or less. You see the logic there?
Philips B5 or the upcoming E6 may be a good contender. But both does sacrifice features. In my experience with the HTL9100 which basically is the same as the B5, the RT5 sounds better in tonal balance. Say all you want about the small drivers, but the real center channel provides a fuller, weightier mid than what the phantom B5/9100 can only achieve.
I'm happy with the RT5, I don't think it is a disappointment when you take its price and features into account then compare it in relative logic to what is available out there. I whole heartedly recommend the RT5, it IS a good true 5.1 system, not a pseudo 4.1 with virtual surround effects.