I know it's a tad late but I just got my copy of Hell's Gate and I would say it's superb (the book is quite huge). The account of the battles inside and outside of the Tcherkassy pocket were the best so far I had read (the account of Battles of Tcherkassy I read pre-Hell's Gate were from Paul Carell's classic, Scorched Earth).
The stories about how the German forces at Lysanka managed to hold out despite repeated pressures of Soviet forces knowing that the Tcherkassy pocket survivors would depend on them for the breakout were superb as well as the individual accounts of the survivors
I'll give it 5 stars out of 5
Apart from this, I only had a small comment regarding the photos. I found that the photos were somewhat "imbalance". For example we have huge size of portrait photos of the individuals involved in the Battles of Tcherkassy but those dramatic photos of the actual breakout were made "smaller". I understood that the author may not used all the photos taken by Adolf Salie (the SS kriegsberichter who participated in the breakout) as well as from Alois Jarolim (the Wiking kriegsberichter who was with the division when it breakout from the pocket) but it would be nice if we could get all those photos but of course this is only my personal preference and I may not be privy to other factors that author may have faced such as cost concerns, lack of space etc.
Notwithstanding, I think this is the best account of Tcherkassy I had read and the best "live-action" book I got so far :)
One more last question. Does the author speaks German? Because at the epilogue section where he mentioned that he travelled with several Tcherkassy veterans back to Ukraine for a visit and to what I have known, Fernand Kaisergruber, the Walloon veteran of the breakout does not speak English