With the latest update to the Google Now Launcher (and the Google Search app, which controls much of the content therein), folks running a device on Android 4.1 to 4.4 will now see the same Material Design styling as those who have the launcher installed on their Lollipop device. Prior to this update, installing the Google Now Launcher from the Play Store would give you a version that was tailored to look similar to the version of Android you were running — now you get the same look no matter what.
Things won't change dramatically if you update and are on a non-Lollipop device, but you will notice that the Google Search bar at the top of the launcher has a nice white color and animations have a bit more life to them. You'll also notice that the Google Now area of the launcher has a slide-in panel on the left, which lets you switch accounts, set reminders and change Google Now settings.
If you're looking to get the most Material in your life but haven't yet updated to Lollipop, you'll definitely want to snag the latest version of the Google Now Launcher and Google Search app (linked above) for the full updated experience.