What is possible with Eclipse is
.1. import the project as general project
.project
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>OpenSpritz-Android</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
</buildSpec>
<natures>
</natures>
</projectDescription>

.2. Put 2 Eclipse . file into modules into /OpenSpritz-Android/app/src/main and /OpenSpritz-Android/lib/src/main

.project
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>OpenSpritz-Android-app</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>com.android.ide.eclipse.adt.ResourceManagerBuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>com.android.ide.eclipse.adt.PreCompilerBuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
<buildCommand>
<name>com.android.ide.eclipse.adt.ApkBuilder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>com.android.ide.eclipse.adt.AndroidNature</nature>
<nature>org.eclipse.jdt.core.javanature</nature>
</natures>
</projectDescription>
.classpath
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="src" path="java"/>
<classpathentry kind="src" path="gen"/>
<classpathentry kind="con" path="com.android.ide.eclipse.adt.ANDROID_FRAMEWORK"/>
<classpathentry exported="true" kind="con" path="com.android.ide.eclipse.adt.LIBRARIES"/>
<classpathentry exported="true" kind="con" path="com.android.ide.eclipse.adt.DEPENDENCIES"/>
<classpathentry kind="output" path="bin/classes"/>
</classpath>
.3. Import as Existing Android Code into Workspace

you can then browse code in familiar way, but
even after that you won't be able to run with Eclipse ADT.
.4.
But you can run build and tasks with gradle CLI or Nodeclipse/Enide Gradle for Eclipse

What is possible with Eclipse is
.1. import the project as general project
.project.2. Put 2 Eclipse . file into modules into
/OpenSpritz-Android/app/src/mainand/OpenSpritz-Android/lib/src/main.project.classpath.3. Import as Existing Android Code into Workspace
you can then browse code in familiar way, but
even after that you won't be able to run with Eclipse ADT.
.4.
But you can run build and tasks with
gradleCLI or Nodeclipse/Enide Gradle for Eclipse