I'm a regular user. I used to be a daily user. Here's a couple of observations:
1. In the morning peak, the up Charing Cross service having two dedicated platforms (8 and 9, either side of the island) is much better than the previous dedicated platform 6 + dedicated non-platform loop, plus the use of platform 5 (blocking that for down trains). Exit of customers alighting from trains on to platforms 8/9 and down into the concourse for London Bridge area / the tube / Cannon Street is far less of a scrum than it was. The bridge was seriously overcrowded, and pretty dangerous, before. And the tunnels were even worse.
2. Separation of Thameslink is great (obviously). There were no Thameslink services in the peak before, at all.
3. In the morning peak there is no longer any need to stand on the bridge trying to guess between platforms 2 and 3 (separate platforms and staircases), to get to Cannon Street (for people transferring from Charing Cross / Thameslink / Southern). This was a major problem, and often resulted in wrong guesses anyway. All Cannon St services in the morning peak now go from island platform 2 / 3. Easy.
4. in the evening peak, the dedicated use of island platform 6 and 7 for services from Charing Cross is far better. Previously trains would get swapped between platform 5 and 4 at short notice - resulting in a mad dash over the bridge, which was already crowded. And often missing your train. That's gone now.
5. Services from Cannon St in the evening peak use platforms 1 and 2, which are not on an island. This is less convenient than the previous island arrangement, though it doesn't seem to cause too many issues (I haven't seen many late swaps of platform)
6. Transfer times (from Charing Cross. Thameslink and Cannon St services) to the Underground do seem a bit longer, but we are probably only talking 30 to 60 seconds. And it's far nicer and less stressful. There is just a lot more space.
7. The Southern side could probably do with one more platform and suffers a bit from three approach tracks, rather than four as before.
8. The platform canopies go all the way down the platforms. I'd have preferred an overall roof in the middle, but at least you can wait on the full length and not get wet now (though the canopies are a bit high so it's not perfect).
9. Exit from the SE / TL platforms via two escalators / two stairs / one lift to the concourse, and being in the middle of the platform is far better (and safer) than the tunnel exit right at the London end, combined with the dangerous / crowded stairs.
On the down side, there is not really enough space on the CHX, TL and CST platforms for waiting passengers; it can still get busy (everyone still bunches, despite the design). This could have been (partly) fixed by covering over the staircase / escalator holes. Also, the stop signs for 8 car trains are in poor places. They are exactly 2/3 down the platform, resulting in (often) four carriages of passengers running down the platform when they realise what's happening and all getting into coach 1. This is really a demonstration of how Network Rail doesn't understand customer behaviour, and is really easily fixed.
On the plus side, there are far more facilities; and there is far more access to the surrounding area; and there is far more space for when train issues stack up (remember the overcrowding a few years ago?).
Anyone wishing for a return to the past really has no idea.
