It is definitely impressive. The Flankers they fly are also modified for airshows - no radar, less than half the fuel load and added weight on the aft center station (see the big single missile on the belly?) That's the only way to get the jet to do all that airshow stuff.
Still, it is very cool as airshow acts go. Tactical relevance is about as cut and dry as asking what the best kind of GA airplane is. It really depends. If you are planning on getting into a turning fight, having a Su-35 is a great start. It has to have weapons to match it's skill or at least compliment the jet's strengths. Those that say visual maneuvering/dog fights are a thing of the past are misinformed about the nature of modern warfare - specifically the legal/political side of BVR engagements. Odds are that we'll end up in a visual fight because we aren't allowed to shoot BVR based on the ROE. So, if that's the case then having an awesome BFM platform is a total upside. The maneuvers it's showing in the show wouldn't be possible with a combat loaded jet (missiles, pylons, radar, etc) but the show demonstrates the maximum that you could do with the airframe. True it can't do the airshow stuff in a real fight, but at the right configuration it could do a lot of stuff that most other jets couldn't hang with.
The whole Flanker family is a very dynamic series of jets. One thing that most US fighter pilots love about the jet is that it carries loads of fuel (longer missions and combat radius without needing tankers). As with anything in aviation, nothing is free. The price you pay is that if your Flanker is full of fuel it's about 1/2 as maneuverable as it could be at a lighter weight. Max G is limited, AoA is limited, etc. So if you get in a fight with a heavy Flanker you are going to have an awesome day - if you meet a light weight Flanker you are more likely to have your hands full depending on the pilots' skillset.
Regardless of the adversary, we want to engage BVR to the max extent that we are able. Visual fighting is very difficult to come away scott free. When people are that close to each other anything can happen. Just because he's turning better than you (or vice versa) doesn't mean you both can't get a missile shot off; then you both eject (best case) and fight it out with knuckles or pistols when you land under parachute. It will be a messy day for sure. We need to keep our BVR advantage; adversaries are gaining ground by the day.
