After trying out a couple, here are the best three alternative gallery apps for Android Lollipop:
Security features such as password/pin protection of the app, hidden folders etc. are also present with the usual slideshow and media player which seems to play a number of video files. You can also perform simple edits like cropping and rotating. Overall, this is a perfect gallery app that I can't complain about.
Photos from online servers such as Google+, Flickr, Facebook and Dropbox can also be added. A special feature that is included is the "Cast" feature which probably allows you to cast your photo or video on a screen that has Chromecast connected to it. If you get bored, slideshows are also a bit interesting in Cyanogen Gallery.
You will get all the original features like the layout as well as the editing and sharing features if you decide to stick with this app. But only use it if you do not mind the always displaying advertisements.