Radiant Dawn is a game that heavily builds on the game before it and that's what helps it become a grander sequel
Course, not everything is great with Radiant Dawn, and it does have a lot of glaring issues. For one, it's a hard game. Even Fire Emblem veterans like me don't have an easy time with this game because of how hard it can be in the beginning and near the end. It's not just hard, but it also doesn't steady its difficulty, some chapters may take you forever and others will be a breeze. Radiant Dawn just never quite cuts the player any slack, and it's quite maddening to play through a whole chapter in one sitting just to see one little thing get screwed up, and making you start over again. Luckily, Radiant Dawn covers such a cruel fate with the new addition of battle saves, and something that truly saved my sanity. For the first 6 chapters I didn't use battle save, assuming it was only a quick save, but once I found out how useful it was, and the ability to abuse it was present RD suddenly did a 180 on difficulty. Now instead of getting headaches over chapters, I was getting them over leveling up my units, the way I normally play.
The other issue RD presents is the availability of units, something not present in most fire emblem games. The vast majority of your units won't be around for most of the chapters so there is a lot of micro managing in terms of who gets to use who, which units should be used, and not always being able to use people that you want. The main problem, in all honesty, is that RD just has too many good units and you kinda want to train them all, but you only get some much time with each of them so then you have to quickly narrow down who you train. Many units even suffer greatly from their short usage, and end up being nearly improbable to use. Also thanks to the great deal of units, many of the supports that were once there to give great detail about characters are now nothing more than an add bonus and a generic dialogue tree. This really did disappoint me greatly as supports are one of the best aspects of fire emblem. Supports gave the characters depth, and reasons to like them more, so we get angry more when they die on the battlefield.
In spite of all these issues though, Radiant Dawn really just ends up being a different beast of a fire emblem game. Sure, RD still has the same old level up systems, the same old weapon system, and the same old animations. Pretty much everything that made fire emblem good, stayed good in RD. But the thing that is ever present in RD, and what separates it clearly from other fire emblem games I have played is how grand it is. Everything is set in a grander scale; chapters are far longer than they used to be; the amount of units you have far outclass any fire emblem game I have played; and the story expands even between two games. Radiant Dawn feels like it was an experiment of how big a fire emblem game can be, and for that I thank it and wish more of it.
Conclusion: At times Radiant Dawn can provide to be too big of a mess of sorts, with its odd sense of difficulty, support system, and choosing which characters to exactly use throughout the game. But if you invest time in Radiant Dawn it will provide you with a grand experience, with a story, cast of characters, and game that match that.