It has taken me a few weeks but I finally read the whole thing, and here is what I think:
I'll divide my review into three seperate parts... comments, questions, and quams. Comments will be things I like about the story, questions will be things that stuck out in my mind that I would really like to ask, and quams are things I don't like about the story. I have five of each type.
Note: This review may be quite penetrating, but it does not imply I don't like the story - I'm merely giving the best feedback I can offer.
Questions:1) Where did all the fast-runners come from?
In the original Land Before Time and through all 13 movies and the TV series we only meet 5 fast runners, and they are Ruby and her family. This leads me to believe that they are denizens of the mysterious beyond and are also few and far between (compared to entire herds of spiketails and longnecks). As far as we are led to believe they do not live in the Great Valley...where did they all come from?
2) Who is the General of the Great Valley?
In wartime there is guarenteed to be disagreement between leading parties... so somebody has to be appointed the general otherwise nothing gets done. Even in the Matrix where the free human city is govered by a council they still appoint a general to oversee the army and make strategic decisions. Perhaps the reason the Great Valley was taken by the forces of Claw was that they lacked a good command structure?
3) What race is Ms. Maia and what does she look like?
I don't reconize the race you are refering too... my knowledge of dinosaur types is incomplete
4) What is a sickle-claw and how is it different from a fast-biter?
Again I don't know what your refering to here though I have a pretty good idea.
5) Why do Strut and Ozzy hate each other so much?
Ozzy and Strut are brothers and even if they fight sometimes it did not make sense to me why they would want to kill each other so bad. And the part where Strut tortures Ozzy? Even in the American Civil War when brother fought brother they still had the respect to not torture each other in the sadistic manner I saw here. Do they have issues or have things just reached the breaking point?
Comments:1) The Great Valley sure didn't mess around with the Claw threat
I liked how well the Great Valley mustered for war when clearly the situation demanded that sort of action. It was interesting to view how the different divisions were organized and the types of drills that they performed. The formation of a Great Valley airforce made sense, and I could certainly see Pternao commanding it. Well done!
2) The Technology of Claw and the Great Valley
An interesting and well written point is how each faction depends on their weapons development to give an edge in the conflict. Mr. Bigmouth is the key alchemist for the Great Valley and even the bad guys have their techos who invent and work with fire and poison. Since the two sides also have differing military forces (Claw enjoys the natural advantage of being built to hunt leaf eaters) the Valley forces have to catch up with a slight technological advantage. A nice Allied-Soviet thing going on here! (forgive my Red Alert reference but it is my thing) I look forward to seeing how the weapons each side procures advance - especailly since Claw has a superweapon.
3) Well done Original Characters
Twlight Valley has a ton of characters... I won't lie. When it comes to the good ones and the bad ones you have things mapped out pretty good. I just love Theta and Hasta simply because I have a soft spot for evil lieutenants...kinda like Lieutenant RJ in Tiberium Wars. They aren't evil but they are damn good fighters and probably the coolest bad guys. Ms. Maia is delightfully evil... I always get a kick out of her. Deimos and Raptix are nice additions to the good guys and also serve to point out this is not a Sharptooth vs. Leaf Eater war but a Claw vs. Great Valley war.
4) Claw Valley's victory in the first battle
This was a good plot twist, as it added the "revenge" element to the Great Valley dinosaurs who have to take back their valley. It also gave a nice change of scenery and added some desperation where previously they had everything they needed.
5) The Addition of a Mysterious Third Side
Three way conflicts always make things more interesting, but inevitably two sides end up teaming up against the last one to take it out before fighting or making peace amoungst themselves. I wonder if your planning something like this.
Quams:1) Out of Character Speech
The Original Characters were done well, but there ended up being so many in total that portions of the story were rushed as you attempted to give lines to everybody, and the ones we know from the movies say things that they would never say if they were in character (compensating for the war setting of course). Examples I picked up on are like this one:
“Well nice to meet ya, Chomper!” Pterano replied.
Pterano would be more likely to say something like "It is an honour to make your aquantience Chomper, but we have little time to dawtle".
2) Named Characters are Invulnerable for the first 15 chapters
Everyone who got killed or maimed in the first 15 chapters did not possess a name, and it got boring after a while to see an endless flow of nameless characters getting killed (and going unmourned despite some truely heroic acts) while the Great Valley goes on like nothing has happened. It especially struck me as odd in the "Battle of the Great Valley" where in the meat grinder of a battle nobody with a name died while lots of nameless soldiers got torn to bits in the name of their Valley. In a war fan-fic where you have a lot of characters, a fair few of them have to die to keep things organized and realistic. If the Claw Valley honestly wanted to suffer no casualties they should have just given all their soldiers name-tags...sheesh!

3) The Dissapearing Gang of Seven
This got me at about the 8th chapter. I suddenly said to myself...hey where the heck is Petrie? Cera? Ruby? They had all dissapeared while the OCs had taken over the action. In a good story it is important not to lose sight of who your main characters are and keep them in the story and doing meaningful things.
4) Paragraphs and Dividers
I just got driven bonkers by this from the get go... the story was jumping all over the place in a single chapter! One line it would be Deimos training and the next Exidium will be talking about his grand plan... with no dividers to show the change of scene. When you advance forward with your story please divide things up so we the readers know when you are changing settings. You can try using this if you would like:
...
And so on.
That is all and I hope you liked my review! In my opinion Twilight Valley has good things about it and bad things but overall it still kept me reading so it qualifies as a success... I would give it an:
8/10
For making a good story out of the brutal art that is the art of war.
Caustizer.