The most succinct way to describe Shin Kyoto Hen would be: "glossed over." What else would you expect from a two hour retelling that attempted to cover 27 episodes of the original series? That's not to say, however, that the OVAs are entirely without merit.
The environments are strikingly beautiful. The characters are modernized: cleaner and redesigned to better suit the current aesthetic, but unfortunately look washed out and unfinished when set against the detail of the backgrounds. Cinematography is done very well; the usage of color and light, particularly contrasting Kenshin's meetings with Misao and Shishio, is a nice touch.
Animation was hit and miss. Where the TV show would use light and sound to indicate a superhuman move being performed, Cage of Flames impresses with full animations; noteworthy in Kenshin’s confrontation with Misao and battle with Chou. The fights in Song of the Light, however, lack the impact of those in the series. (Saitou’s evaluation fight with Kenshin comes to mind.) An argument can be made for the finesse of Kenshin vs Soujiro’s shukuchi duel, but the gatotsu and the futae no kiwami just don’t have the same raw explosiveness.
The soundtrack is still excellent. While the renditions lack their predecessor’s quaint appeal, they are more intricate in timbre and more “cinematic.” Familiar themes are used accordingly and don’t fail to accentuate the mood of a scene or remind us that this is indeed Rurouni Kenshin. Just don’t expect something as amazing as Tsuiokuhen’s OST.
Much of the gag humor and lightheartedness of the series was omitted in favor of a serious tone that accurately reflects the gravity of the arc. Studio Deen was aware of the age of the RuroKen fanbase, and thus had no qualms about showing the brutal reality of the fights and Shishio’s world; things that were implied and understood but not displayed by the series. This is where Cage of Flames truly shows its potential, setting all the scenes for conflict, building tension, and acknowledging all the right events from the original anime.
As if discouraged by the nostalgia-biased criticism of OVA1, the staff seemed to give up in Song of the Light. Sloppy animation aside, every character seems deflated. Both writing and delivery are unnatural given how little the development of their camaraderie is depicted. (I did like the more mature Misao, though; more convincing for the role of Okashira.) Aoshi and Shishio, obviously keeping their desire to strike in check in the first OVA, never demonstrate that catharsis, wasting all the anticipation.
As for how everything plays out... The absence of so many things (and members of the Juppongatana) completely overshadows the version of the story they attempt to tell.
Kenshin and Sanosuke never meet up; Sano is instead exclusively partnered with Saitou.
Sano’s parallelism with Anji is not explained.
Hiko’s arrival at the Aoiya is far less grand, because Yahiko never proves himself against Henya or demonstrates his impressive spirit.
Soujiro’s internal struggle to reconcile Kenshin’s and Shishio’s philosophies is barely there.
Saitou does not show his loyalty to Aku Soku Zan & police fighting Usui.
In fact all the duels that are glossed over don’t take place in Mt. Hiei, even though it was shown in Cage of Flames. I can go on, but the greatest wtf of the OVA and absolutely unforgivable omission is that Kenshin never uses his ougi…every major fight is won handily and anticlimactically. The conclusion of Watsuki’s Kyoto Arc is fundamentally altered and weakened.
*One thing did pique my interest: Saitou didn’t disappear in the blaze; he escapes with Soujirou. What might happen should the prodigy be taken under the wolf’s wing?
And so our heroes return (heroes being Kenshin and Aoshi, wtf happened to Sanosuke?) While Studio Deen apparently forgot how to make shounen/seinen fights epic, they do reunions passably well. (Kaoru finding Kenshin in OVA1, Misao welcoming Aoshi back.)
TL;DR Longtime fans of RK, Cage of Flames is worth checking out. Song of the Light is a waste of the va’s reprising their roles. Newcomers, don’t bother, watch the series, but feel free to stop before the Christian Knights and FengShui >_>