The artwork is definitely the weakest aspect of The Flash #24. Specifically, the pages penciled by Carmine Di Giandomenico. There's been a rough wildness to Di Giandomenico's work in past issues that I thought fitting for depicting speedsters, with random squiggles suggesting continual motion even when at rest. Unfortunately this stylistic choice looks sloppy when paired with the more static figure of Iris West, who appears to be the only figure being drawn "correctly". The excellent pages by Pop Mahn in a more traditional style only add to this feeling that Di Giandomenico's art is sloppy rather than stylistic.
It's a shame because the story by Joshua Williamson is a good one. The mystery of just where (or when) this Reverse Flash came from is an intriguing one. The action scenes are well-written and there's a great buddy bonding moment between Hal Jordan and Barry Allen that reminds me of the better bits of Mark Waid's The Brave And The Bold.
The Final Analysis: 6 out of 10. The story is great but Carmine Di Giandomenico's stylistic choices look slap-dash when compared to Pop Mhan's pages in the same issue.