Personally I do not hardly ever work with Midi (.mid), but often hear people who are looking for software dedicated to the development and modification of this kind of file.
If you are looking for software that is not too heavy, easy to use and without too many features because you are interested to work exclusively on your Midi files, then it might be a good alternative the MidiEditor, developed by Markus Schwenk, who has released it for Windows and Linux, on its website for free .
MidiEditor is equipped with a graphical interface not very attractive but certainly very simple, and structured in a very intuitive way.
On the top, the Toolbar, we note that all the main controls are grouped, on the left we have the classic Piano Roll,in the center the main work area (Event View) and on the right a widget for channels and audio tracks.
The controls in the Toolbar seems to me that they are represented in a very clear way, the icons tell us much known functions: Copy, Paste, Delete, Move, Zoom In and back, and so on.
The most important part is that defined Event View, where we see the representation of the notes whose frequency is identified by correspondence with the keys of the Piano Roll, while its length is suggested by the length of the label.
MidiEditor is also equipped with an editing section of velocity, such that it is possible to give expression to your performances with MIDI file. In truth there are many features that characterize this agile little program, so I refer you to read the manual that you can navigate by clicking here.
If you are convinced for a ride, and you want to download the right version for you, then click here if you are a Linux user (i386), here if you are Linux amd64, then here if you are Windows users. The latest stable version, the 2.5.0, has been released in April 2013 MidiEditor was concerned about a new version every year, so in short we might expect an updated version, taking into account that the developer accepts recommendations and reports of all kinds, writing through the pages of contacts.
If you want to take a look at the official site, this is the link.